Going from normal to angry is not "flipping" your personality. It's called bipolar for a reason: there are two poles, equidistant from a center. It's also called manic depression: when you're not depressed you're often high as fuck.
What you described is called "getting really angry and losing your shit." It happens to pretty much everyone.
EDIT: I probably should have written that like less of an asshole. Sorry - I'm not here to deny your problems. The point still stands though.
Perhaps I chose the word bipolar incorrectly, but it's the closest word that describes the situations I've encountered with my anger.
I guess the feeling is hard to describe; "getting really angry and losing your shit." doesn't cover it at all, especially in the situations I can remember. Everybody looses their cool, this is way beyond that for me. The situations where it's come up wouldn't constitute the level of rage I've felt.
There is a continuum between losing your shit, like normal people do, and having a full blown behavioural disorder that destroys your life. We all lie somewhere on it. There's probably another continuum that goes off in the other direction, with jesus hanging out on the end with master joshu or something.
If you need to put a label on yourself, intermittent explosive disorder or something is likely closer than bipolar.
What you described is called "getting really angry and losing your shit." It happens to pretty much everyone.
EDIT: I probably should have written that like less of an asshole. Sorry - I'm not here to deny your problems. The point still stands though.