I have before don't worry! Dx I had to trim my nails waaaay down so I couldn't scratch at one point...xD I suggest exercise! Especially yoga because it hurts really bad, but it's good for you! Poses like downward dog and the warrior pose...just hold them for a wicked long time. Plus, it helps relieve stress too which is SO awesome.

But yeah, feelin that way isn't fun. Whenever I feel that way if I'm in school or somewhere I can't just run around like a headless chicken I think of all the things I'm thankful for, and why I didn't SI in the first place. That usually keeps me from doing it. Or I talk to a friend who really saved me from something awful a few nights back.
Hang in there! ;-)