Wow, this all sounds like a description of my bipolar except for your description of aggressively cutting off friends and ending relationhips. If anything, during manic phases, my social circle grows. I fiercely enjoy being around people and collect many associates eager to ride the wave. On the contrary, it is during periods of Depression that my circle tightens as I withdraw from everything and everyone. I may even push people away. But never have I cut people off. I've certainly gotten irritable during hypo/mania but never have I raged or been agressive.

I agree this could be a mental health issue. Borderline Personality Disorder perhaps?

A few additional questions. You mention a fluid change of moods ...

- does this person exhibit signs of grandiosity? Are they the 'life of the party'?
- have you recognized any risky behavior (this could be as little as driving agressively to permiscuity to life risking)?
- do they speak rapidly and dominate conversations?
- are they impatient? irritable?