From an early age, my parents (both in the mental health field) recognized small symptoms of bipolar disorder in me -- periods of extreme energy and no sleep followed by lulls where I wouldn't want to do anything. However, they decided that the best course wasn't to do anything about it (or even tell me they had these concerns), as they figured it was just me being a kid. For what it's worth, I think they made the right choice.
I was 15 or so when I started seeing these symptoms for myself, and saw them becoming more extreme. I would spend weeks programming furiously on The Next Big Thing (TM), then fall into an equally low period, which usually lasted about twice as long as the high. Originally in these low periods I just had trouble focusing on anything, slept a lot, etc, but gradually I saw them change into something very different. I became suicidal, and the smallest thing would set me off. If I got into an argument with my parents, I would just think "is all this worth it?" and start spiraling downward. My girlfriend at the time is the only reason I made it through; she helped me realize that this wasn't normal, and that I really should do something about it.
At 16, I told my mom that I wanted to see Dr. D (a friend of the family, and probably the best psychiatrist in our small town). It came as no surprise to me to be diagnosed with bipolar I with rapid cycling; it wasn't uncommon to have extreme mood swings in between the longer periods, even happening several times a day at their worst.
He then started me on various drugs. I don't recall the order or combinations, but I was on -- at one point or another -- lithium, Lamictal, Abilify, carbamazepine, Depakote, and others I can't remember now. None of the standard mood stabilizers worked; I either felt completely numb or was sick as a dog. Lithium in particular made me feel worse than I ever have in my life, emotionally and physically. We tried a couple combinations to balance things out, but in the end the mood stabilizers just weren't helping; in retrospect, though, I wonder if they were and I just couldn't recognize it in myself. Regardless, the next step was anti-psychotics; I wanted to be put on anti-depressants, as the lows were what bothered me, but it was simply too risky -- if they were successful, they could well put me into mania that I couldn't control.
The anti-psychotics made me feel nothing. I don't know how I can explain this to someone who hasn't been there, but it's like your emotions just cease to exist. In theory, they worked, but a complete lack of emotions and creativity simply wasn't worth it. I was 17 by then, and I decided to stop taking all meds. I moved to San Diego for my first job shortly thereafter.
I rode on an extreme high for the first few months I was there, working 18+ hour days. I was a 17 year old making more money than he should've been, and I took advantage of it. Sex, drugs, and rock and roll really describes it well. I went to shows, I met a girl (whom I took a cab to every weekend, an hour and a half each way, then got engaged to a month after we started dating), drank a lot, etc. In short, I did everything that someone in the throws of mania would do. It took a while for this to catch up to me, but as always with bipolar, it did. I crashed hard, and if it weren't for my fiancee at the time, there's no way I could've made it through. I frequently thought about checking into a hospital, but I thought I needed to push through. I'm not sure if I made the right decision or not, still.
It took me a long time to really get myself in balance. The first step was to recognize what state I was in -- this is remarkably difficult. The next step was to learn how to bring myself back to normal when I started getting low, and I became quite good at it. Ignoring a few small fleeting thoughts, I haven't been suicidal in about 4 years. Then I learned how to embrace the manic side of it, and put it into my work without letting it go too far; I don't know that I ever really got very good at this, as my first two months in NYC have shown me lately.
A combination of a good support network (key for everyone, IMO, not just those suffering from mental illnesses), knowing myself, and knowing when to say "no" has been crucial in me largely stabilizing myself over the past few years. It's not perfect by any means, but it's working better for me than anything else has.
To close, I want to impress upon everyone the importance of getting help with mental illness. This doesn't necessarily mean medication (it certainly didn't in my case, even thought it was tried), but just knowing yourself is insanely important. Too many people refuse to get help, and end up in far worse place. I'm happy with my life as it stands, but it could easily have not gone this way.