This is really interesting. I get the same urges from time to time to cut my hair or shave it really short. I also have trichotillomania so I kind of justify it to myself on the grounds that if it's very short then I won't be able to pull, and maybe next time it will grow back thick and lovely. I've never thought about it more generally in connection with extreme moods so it is interesting to hear from lots of people here who apparently don't all have trich? I think I also have psychological issues of wanting to make myself deliberately look awful to match the awful way I feel inside.