Hi

So, I got a new doctor. I just recently moved and so had to get a new one; mostly because my old doctor would be too difficult to see due to travel limitations. Anyways, I went in today and got a brand new diagnosis which is kind of overwhelming for me.
He basically told me that upon review of my records and my symptoms, coupled with the random factor that a medication he had initially prescribed to me for sleep (an anti-psychotic, seroquel) ended up helping me a great deal with other issues it hadn't been prescribed for, he had come to the conclusion that I have bipolar disorder. I was a bit skeptical at first. I had been, for a long time, told that my issue was with paranoia, depression and anxiety. So, with this previous knowledge, I cocked an eyebrow.
He went on to explain further. He told me that my predominant depression was a major symptom but the fact that I was paranoid, and that the paranoia manifested itself in episodes, was actually a symptom of mania. I didn't know that before.
I have, from time to time, experienced these episodes ranging from anywhere between a couple days to a couple months. Normally I would be depressed. If I wasn't depressed I would be super productive, optimistic and feel capable of anything. I sometimes feet like I can change the world. Like I alone could make such an impact that I have a responsibility to do so. I felt like I could save the world from itself, if only people would listen to me. I guess that's a bit grandiose and unrealistic though. I usually rotate between being depressed and feeling "up" in the way I just described. From time to time though I would experience something else altogether; something darker. Reflecting on it, I've found that it almost always follows a certain formula - a linear progression of feelings and events. First, I would become paranoid and irritable out of the blue. I would usually start to isolate myself and withhold emotions from the people around me. During these periods, much like I would when depressed, I would often drink like a fish. This always made it worse. It would start to snowball over time; my paranoia would become worse and worse, to the point that I would almost be delusional. Everyone was against me, there were forces and people (sometimes people I knew, sometimes people I didn't) working against me, trying to hurt me; howling for my blood. I would keep this to myself. These suspicions and my feelings of hurt and fear, after all: if I showed weakness, my hidden, potential enemies would jump at the chance to use that against me. Everyone was just aching to kick me while I was down. Everything would become suspect. People's motivations would always be dark and every action or statement held some underlying menace. I would feel alone and attacked by everyone and everything; like a wild animal backed into a corner. Eventually the frustration would overwhelm me and I would climax into a psychosis: becoming hostile to the point of lashing out. This was mostly verbal but has in more serious cases turned towards unprovoked violence. I would then come down afterwards. I would get depressed again and be full of regret and shame. I would hate myself and think that I was a nasty, vicious person - undeserving of basic human necessities like happiness. I would lay in bed and barely move for days, obsessing over people I hurt and things I had screwed up. It was like a cycle.
My doctor told me that this was not in fact paranoia by itself. It was a symptom of bipolar disorder called dysphoric mania. He went on to explain that it was a manic episode - much like the ones I have where I felt like I'm almost messianic. Except that instead of being on a positive spectrum and feeling like everything was fantastic, that it was negative in nature. I don't know. This whole revelation has overwhelmed me in a big way.
I am having trouble coping with this new information. All of these questions I have, all of the things that it explains... Thinking "what if?" What if I had known earlier - could I have prevented myself from doing things to sabotage my life? What if he is wrong? When I do feel well, is it only an episode caused by an illness? Where do I go from here? Will I ever truly be well; ever truly be healthy?
I am scared to tell my girlfriend. I don't know how she will react or if she will take it seriously. I hope she will understand, and I honestly think that she will. She is very understanding and I know she loves me a lot; enough to put up with my mood swings and my bullsh*t. I am just worried though. I don't handle changes well, so being told that everything I thought I knew about my problems was wrong is a big, jagged pill to for me to swallow.

All I keep thinking is "*****. What now?"
Is there something you guys do that helps you cope with this kind of stuff? I am very open to some positive suggestions right now.