I am not short tempered but I know the feeling of "this is not me". For example right now I want to be quiet and recover from my cold. But there is this wiredness that keeps shouting: go out, smoke, get drunk, meet people, life ist too boring, move!

This is definitely not me saying this right now, but I guess it's hypomania.

I also experienced this "not me" feeling when I was depressed and thought about killing myself nonstop and I know I would NEVER kill myself. These thoughts were just not mine and I recognised them as "foreign" the moment I thought so.