Same thing here. It doesn't have to be a "big" thing to make or ruin my day. For example, if I say hello to the clerk and she doesn't say hello back ... that makes me depressed, all the bad thoughts come up, I just want to go home and die there. And then I go to another store and I say hello to another clerk (if I do, I normally don't after one "rejection", though)... and she smiles and says hello back. And that makes me feel very happy and confident. I just go from one mood to another very suddenly, just like you ... about 6 times per day.