The situation to which I refer involves a person who has had an accident and their recovery was going well then not and it keeps changing. I am trying to warn someone caring for them that the situation can change quickly without notice and I can't think of the idiom to describe the speed and unpredictability of that potential change so that they will take nothing for granted.

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    What's wrong with 'sudden' or 'suddenly'? Commented Apr 19, 2021 at 20:33
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    If I were trying to direct someone how to give care in a potentially life-critical situation, I don't think I'd rely on an (unfamiliar?) idiom to express it... I'd suggest using however many very descriptive words are necessary to convey exactly what you want to describe. ( Then come back here and have some fun learning new idioms once the patient is in good hands )
    – A C
    Commented Apr 20, 2021 at 18:02
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    The question does not give an exact enough specification of the condition of the patient. It's crucial to specify whether the patient liable to die at any moment, and how serious the injuries sustained in the accident were. Commented Apr 21, 2021 at 8:49
  • Though not a complete answer, the word "overnight" describes the scenario you describe. I guess you could call the word an idiomatic word, but you'd likely need a bunch of other words to accompany it. Example: "The patient's condition could change dramatically overnight." Commented Apr 21, 2021 at 14:23
  • The situation is "fluid," "dynamic," "volatile"-- take your pick. As far as idioms go, you might say that the person's situation is "touch and go, "can to turn on a dime, "is up in the air and can change out of the blue." Commented Apr 21, 2021 at 15:10

16 Answers 16


I do like the other answers as well. I guess in such a situation, you'll want to be more detailed and sensitive about the condition, but if you're looking for a one word description:

MW 1 a: characterized by or subject to rapid or unexpected change

Though correct, this might sound a bit too technical and cold in the context of the health of a human being.

  • Note that volatility has a very explosive connotation, literally and figuratively. It's not just rapid or unexpected change, but specifically implies a large change.
    – Flater
    Commented Apr 20, 2021 at 15:58
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    @Flater it doesn't imply explosive to me nor large. It implies a change that is both fast and counter to the current state (usually negative)
    – Matt
    Commented Apr 20, 2021 at 16:04
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    Note that the OP is asking for an idiom.
    – Joachim
    Commented Apr 20, 2021 at 22:29
  • I don't think OP is specifically tied to an idiom so much as something short and to the point so they don't need a paragraph to describe it, which an idiom might accomplish. This word also does that perfectly. Commented Apr 22, 2021 at 19:21

One phrase that fits well for this situation is touch and go - it means that the outcome of a situation is uncertain, and that things can change at a moment's notice. A person in the hospital after a severe accident may be in "touch and go condition" if it's unsure if they'll survive, and it can be used to highlight the unpredictability of the outcome even if it seems they are getting better. A situation that is "touch and go" can change rapidly and dramatically.

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    It's also used to describe a certain kind of flying exercise -- touch-and-go landings, where the pilot touches down and then takes off again on the same pass down the runway. Commented Apr 19, 2021 at 21:14
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    Close, but it does not deal equally with good and bad outcomes. It is usually used in circumstance where one is more aware of the bad than the good.
    – Anton
    Commented Apr 20, 2021 at 7:27
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    @JohnLawler Interestingly, the phrase has an even earlier origin, with the connotation of describing a precarious situation dating back to the 1800s, when stagecoach drivers might narrowly escape a catastrophic collision if it was only a glancing blow - the carriages would literally "touch and go", although the outcome of any collision was uncertain and could turn out very differently. Commented Apr 20, 2021 at 16:47
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    @Anton Yes, making it common for injuries. They aren't going to suddenly close up wounds, but could suddenly get much worse. My only concern is "touch and go" often implies they could die. Commented Apr 20, 2021 at 20:58

Medical parlance when talking about someone whose condition is not getting any worse is, "stable." You often hear this in news reports after someone is injured, "Doctors describe the victim's condition as critical but stable."

While it would probably offend a doctor's sensibilities to describe a patient's condition as, "unstable," from someone who wasn't a doctor the meaning would be clear.

d(1): liable to change or alteration

A medical professional would probably use the phrase, "Their condition is not yet stable," or, "We are trying to stabilise them," mostly to avoid the implications of the word unstable and it's association with mental health.

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    I think it would be against their sensibilities not for its confusion with mental health, but just because "not yet stable" is a more positive outlook than "unstable," and reflective of doctors' agency/expertise. I can imagine them using the former when they want to encourage hope, but preferring the latter if they want to argue against an irresponsible discharge. But I'm not actually familiar with the ER side of medicine so take it with a grain of salt :)
    – Feryll
    Commented Apr 20, 2021 at 9:56
  • @Feryll, that's a fair point. Commented Apr 20, 2021 at 9:57
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    Doctors (for various reasons) don’t like to express negative attitudes. Just as a simple example, if there’s a 96 percent chance that a patient will die, they say that the patient has a 4 percent chance of surviving.
    – jmoreno
    Commented Apr 21, 2021 at 14:48
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    An old Saturday Night joke went "Generalismo Fransico Franco is still dead. His doctors describe his condition as 'stable'". I think there's a risk when you play with that word it may seem like you're trying to be funny, as in a coma is stable. Commented Apr 21, 2021 at 17:19
  • "We need to stabilize him", "He is not stabilized". Or the null statement "He is in critical condition" without saying stable. Kinda wierd, I know.
    – Scottie H
    Commented Apr 22, 2021 at 20:29

The situation is 'hanging by a thread':

Be in a highly precarious state.


to be in a very dangerous situation or state : to be very close to death, failure, etc.
Example: The patient's life was hanging by a thread.

Dictionary.com gives a few more examples, and the origin, emphasizing that this idiom fits your prerequisite of the change being able to happen "without notice or reason":

Also, hang by a hair. Be in a risky or unstable situation, as in His promotion was hanging by a thread, or With the lead actor sick, the success of our play hung by a hair.
This expression, already proverbial in the early 1500s, alludes to Damocles, who vexed King Dionysius with constant flattery. The king invited him to a banquet where Damocles found himself seated under a naked sword suspended by a single hair, symbolizing his insecure position at the court.


When things can change course rapidly, one expression is "to turn on a dime." In general, the phrase "Life can turn on a dime" or "Life turns on a dime" applies to the big picture to include appreciating what you have and how things can change at any moment. Change can go in different directions, so it's not necessarily a foreboding phrase as much as it marks an abrupt switch. You could say someone's behavior turns on a dime when the changes are sudden. (TFD)

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    Do they say "turn on a dime" in the UK?
    – GEdgar
    Commented Apr 20, 2021 at 0:22
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    @GEdgar I wondered about that as well and saw in comments here that "turn on a sixpence" refers more to the literal manœuvre on which the expression is founded. Worth asking....
    – livresque
    Commented Apr 20, 2021 at 0:31
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    I like this one because it refers equally to good and bad outcomes and it refers to an almost instantaneous change.
    – Anton
    Commented Apr 20, 2021 at 7:25
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    UK equivalent was "turn on a sixpence". Although I've grown up with decimal currency, that phrase remained current for at least a few decades after the switch (and sixpences were legal (2½p) until the mid-1980s, though I never saw anybody use one). I believe it's still understood (but I'm too old now to know what the Young People say...) Commented Apr 20, 2021 at 8:32

His condition is on a knife-edge.

on a knife-edge [phrase]

To be on a knife-edge means to be in a situation in which nobody knows what is going to happen next, or in which one thing is just as likely to happen as another.

[Collins Cobuild]

There is at least a strong connotation of impending disaster:

on a knife-edge (also on a ˈrazor’s edge):

in a very dangerous or difficult situation where there is a risk of something terrible happening:

  • He was balanced on a knife-edge between life and death.

[Farlex Partner Idioms Dictionary]


To say that things are "up in the air" seems to covey this meaning, a situation in which many factors are at work and it is impossible to predict how things will resolve themselves. At the same time, there is a sense that some sort of resolution is imminent.


The most common way to describe a situation that changes frequently and unpredictably is to say that "the situation is fluid".

I don't think this sort of thing is what you are really after, though, because the patient's condition is not really a situation. Sure, it creates a situation, but to warn about the instability of that situation instead of the instability of the patient's condition shows a self-centered disregard for the patient.

I think the most common way to warn your caretaker would be to say that the patient's "condition is unstable".


Lots of good answers already but I'll add:

The situation is fragile.


  1. ADJECTIVE If you describe a situation as fragile, you mean that it is weak or uncertain, and unlikely to be able to resist strong pressure or attack.[journalism] ...moves that will place added strain on an already fragile economy.
    The Prime Minister's fragile government was on the brink of collapse. His overall condition remained fragile.


The idiom I would use to describe someone who is (perhaps) recovering but the situation could worsen at any time is

not out of the woods yet

"Despite improvement, not yet completely free from difficulties or danger. Often said in reference to someone's health or financial situation." [The Free Dictionary]

So you could counsel your friend that it's great that the patient has shown signs of recovery but that they are not out of the woods yet.


Others have given good answers—I'm particularly fond of "touch and go," but only if the recovery is a life-and-death matter—and another more poetic and general expression I could give similar to "can turn on a dime" would be "[prone to] vicissitude," e.g. "the vicissitudes of an itinerant lifestyle."

A less highbrow version of the same is "ups and downs."


A lot of the other answers are good if you want to imply the situation is more bad than good. Eg "touch and go", "hanging by a thread". If you want to illustrate uncertainty while not favoring either direction a common phrase is "it could go either way". It's good for situations where you might use the phrase "knives edge" but don't want to sound so dire or dramatic.


I would not rely on one idiom for the message you are trying to convey. I'm not sure there is one that fully carries the idea, and it's an important message that you don't want to be misunderstood. I would just say something like what you said in the question:

Don't take anything for granted when you're taking care of [person]. They can seem fine one minute, and just a bit later their condition can be much worse. [And you can be more specific than just "condition can be much worse."]


The generic most commonly used idiom to describe this situation is Anything could/can/might happen

Any outcome is possible The Free Dictionary

Anything's possible Cambridge Dictionary


There's the commonly used, "We'll just have to wait and see," which doesn't lean to a positive or negative judgement.

It's first seen in Daniel Defoe's Robinson Crusoe (1719): “We had no remedy but to wait and see.”

  • "Wait and see" means that we cannot predict the outcome but doesn't imply (to me at least) that the 'medical situation is likely to change all of a sudden without notice or reason'. Commented Feb 19, 2022 at 17:58

The person's status is "in flux" or "fluctuating".

From Cambridge Dictionary:

flux (noun): continuous change:

Our plans are in a state of flux at the moment.

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