I think feelings are just feelings. You wouldn't say "pain" lies and it's a feeling. But people have words and one cannot think without using words so when one thinks about feelings, the descriptions or attributes one ascribes to feelings can be not correct. The minute we say, "I'm sad because. . ." we are using the feelings.

Feelings can be elicited in the moment, by something that is happening now or, later, when we are thinking something that reminds us of something else. I invented an entire fantasy world I lived in and when I tried to get rid of it by killing off the people inhabiting it, it was very painful and I cried. Was I really sad and distressed? Yes. But there was no real event that caused the sadness; it's similar when we watch movies or read books, etc.

So, there may be no way to know why you felt sad and small; we are often anxious in dreams (I had an aggressive poisonous snake in mine last night, chasing me and it originally came out of my bed blankets, etc. in my dream the night before!), sometimes happy or sad and I've had dreams that I can only describe as "dreary" where I woke feeling as if I were depressed; your sad and small may be like that, part of an almost unconscious thought or image that flashed across your brain and then was gone. You know how babies sometimes are thought to smile but have "gas" instead? Something like that?

I believe feelings are a lot like thoughts; they can be useful or ignored if we don't find them useful, but the more aware of them and the better we learn to deliberately use them to help us function, the smoother our life goes. I believe unpleasant feelings don't have to be used; they can just be "oh, there's that. . ." and then moved one from if possible. With the sad and small feelings you describe, I would have done something that that with them, said to myself, "curious, wonder where these came from" and, not finding anything, gone on to either another subject or found a sad/small feeling subject to explore that I used the feelings as a stepping stone to but which wasn't necessarily related to them; whatever I was feeling like working on at the time.