How can I use the verb “sad” in the past continuous?

Question

How can I use the verb "sad" in the past continuous? E.g.:

I was crying.

I was missing.

What should be the sentences for sad or upset in past continuous? Why do some words like the two above not follow standards? Are these exceptions?

Answer 1

Sad is an adjective, so it doesn't have a past form. You'd just say:

I was sad.

There is the verb sadden, however.

I was saddened.

Upset can be a verb, but it's an irregular one. Its simple past (and past participle) form is upset.

I was upset.
I was upset by the news.
The bad news upset me.

Note that both sadden and upset are transitive verbs. (The intransitive usage of sadden is archaic.) So if you are going for past continuous, simply saying

I was upsetting.
I was saddening.

wouldn't really work — it would raise the question, whom were you upsetting/saddening? So instead, you would have to say

I was being upset (by something).
I was being saddened (by something).

Answer 2

There is no verb "sad" in English. It's an adjective. The closest you can get is "feel sad", which you can put in the past continuous:

I was feeling sad.

Similarly, you can write

I was feeling upset.

Answer 3

Cry and miss are two verbs; that is the reason you can say "I was crying" or "I was missing."
Upset is also verb, but it means "to make others unhappy;" if that is what you mean, then you can use the past progressive of upset like you do with other verbs.
Upset and sad are two adjectives, in sentences like "I am upset" or "I am sad." If you want to use the past progressive, the verb in those phrases is to be, whose present participle is being. I have never seen somebody using the past progressive in that way, though, when you can simply write those phrases with the simple past.