From the ever-informative Wikipedia:

Signs and symptoms of the depressive phase of bipolar disorder include: persistent feelings of sadness, anxiety, guilt, anger, isolation and/or hopelessness, disturbances in sleep and appetite, fatigue and loss of interest in usually enjoyed activities, problems concentrating, loneliness, self-loathing, apathy or indifference, depersonalization, loss of interest in sexual activity, shyness or social anxiety, irritability, chronic pain (with or without a known cause), lack of motivation, and morbid/suicidal ideation.

Interestingly enough:

A number of recent studies have observed a correlation between creativity and bipolar disorder, although it is unclear in which direction the cause lies, or whether both conditions are caused by some third, unknown, factor. It has been hypothesized that temperament may be one such factor.

Can't say I'm bipolar, but I definitely have pretty severe mood swings from time to time. And I have noticed that when I'm miserable, I'm more productive and creative. I've often wondered if I have a self-sabotaging nature to dilute any chance of complacency which would continue to mire me in mediocrity.

Man, I'm so white.