I don't know why this keeps happening, is it anxiety, or something else?

[Applecherry]

In the last 2 months, like from mid June, to early August, I've had severe anxiety, like kind of a nervous breakdown.. I dealt with the severe anxiety for so many weeks, I was afraid to even go out shopping for fear of more attacks. Then for whatever reason, I started to feel a bit better again, I was enjoying life more, and have been able to enjoy going out more again and shopping. and this weekend, I have been feeling pretty good (not great, but much better than what it was).. then for some reason, out of nowhere, I have been getting these thoughts that pop up in my mind, memories of something pretty vague, but the problem is, I can't remember where they came from. I even question if the memory was a dream. It really upset me last night when it happened, and pretty much ruined the rest of my night, cause I kept thinking about it, and wondering if I had dreamed it or if it really happened. it made me feel confused and frustrated. but then after some hours, I slept it off and forgot about it.

Then again tonight, I was hit with another one, and now I feel depressed and upset. It's not so much the thought that's a problem, it's why it is BOTHERING me so much that is the problem, because I have thought in general, I am feeling pretty good..

I don't know what to do to stop being upset about it. Any suggestions?