I've asked myself the same question each time it happened during the three episodes in my life, and this third one has been a real challenge. Its been over a year, the first half was really bad, the rest better with some serious setbacks. I am on medication and it helps, but not as well as in the first two episodes. One thing I have gotten out of therapy is that while we want to ask ourselves "why" and "why me", it doesn't really help us, it leads to more self pity which causes more frustration, anxiety, and depression. One phrase that sticks with me is that "today is not tomorrow" so that can help at times. I'm not saying I'm immune from ever asking the why question even now, but I know there is no answer, this is my cross to bear, and I can only keep trying to look forward, knowing I have found relief in the past and have had good days, even weeks, and parts of days even in this current episode. Keeping a journal may help, its good to see when you are not feeling well that you have proof in writing that you can feel well at times, and with proper treatment of whatever sort, those periods of wellness should increase again. But I do think we all ask that question of why, especially in the beginning when it is like a recurring nightmare, but that will get better even if its sometimes hard to envision when it feels bad.