Looking for a word to describe that moment when you realize everything is falling apart. You are going along in your life and everything is ok and then suddenly, you realize it is really not. This would be for an event akin to you think you're happily married and then your spouse files for divorce; you think your boss is a great, upright person and then you realize they were embezzling money and the company is folding, etc. Not so much for a natural disaster, if that changes any potential answers,
In some cases, cataclysm (“A sudden, violent event”) will work. Also consider:
• crisis (“A crucial or decisive point or situation; a turning point”)
• turning point, “A decisive point at which a significant change or historical event occurs, or at which a decision must be made”
• crossroads, “A decision point; a turning point or opportunity to change direction, course, or goal”
• watershed, “A critical point marking a change in course or development”
Perhaps a bit wordy, but peripeteia?
per·i·pe·te·ia also per·i·pe·ti·a (pr-p-t, -t)
n. A sudden change of events or reversal of circumstances, especially in a literary work.
[from Greek, from peri- + piptein to fall (to change suddenly, literally: to fall around)]
How about wakeup call:
an event that warns someone that they need to deal with an urgent or dangerous problem (often + to do sth) The 1971 earthquake was a wake-up call to strengthen the city's bridges. (often + to ) The World Trade Center bombing has served as a wake-up call to the FBI on terrorism.
Colloquially, you could also say an oh shit! moment.
"Breaking Point" which can cause a "Nervous Breakdown"
Jill reached her breaking point with Jack when she saw him kiss Jane. (She goes through an emotional change and perhaps is forced to change her decisions.)
Jill had a nervous breakdown after she saw Jack kiss Jane. (She goes through an emotional change and loses the ability to cope with her situation.)
Inspired by the other answers, you might be able to use ruin for this:
v.intr. To fall into ruin.
The term that comes to mind for me is earth-shattering, which fits very well with the way you phrased this question. I've also occasionally heard it used in the manner of "Bob's earth was shattered when he discovered his wife was cheating on him," though I can only think of verbal examples, not anything written down.
disillusionment is a word which denotes the feeling of disappointment from realizing that circumstances are not what they were previously trusted to be.
A related word is disenchantment, which is a disillusionment in regard to a person, like to the embezzling boss who brings down the company.
At the very moment when the new information is revealed, there may be a situation in the mind that is described by the psychological term cognitive dissonance due to the conflict between the previously held beliefs and the new information.
I call the moment when the ground falls out from beneath my feet, "take off". There is a similar moment when the ground reattaches itself to my feet and I call it "landing".
The words suggest that it is I that is moving - which is absurd because as we all know I am stationary and the earth is moving relative to me.
I don't think there is a word for what you describe -- though there really ought to be one.
I am going to go with "worldshaken" as a new coining. Anyway, couldn't find any instances in Google Ngrams. So, if it catches on, folks, you heard it here first!
"Observing this incredible event, Sarah was suddenly worldshaken. Nothing was the same any longer."