Bipolar Disorder?

I am really worried that I am bipolar. I am 15, and have been experiencing extreme mood swings since I was twelve. Sometimes I will have strange, out-of-body experiences that I look back and am ashamed of. During these experiences, I become so overcome with depression and/or anger that I slash my wrists or try to commit suicide in various ways (these have both happened various times throughout the years). Occasionaly, but not as often, I will have feelings of pure calm or become overjoyed, and the tiniest incident will bring me spiraling into a downward mood swing... I'm afraid to talk to anyone because my family kind of ignores my behavior and pretends its not happening whenever they walk in on me doing the above mentioned things, and my friends always crack jokes and make fun of bipolar people so I can't talked to them... Am I bipolar and if so, what should I do?