http://en.wikipedia.org/wiki/Bipolar_disorder
To quote the article:
The Depressive Phase
Main article: Depression
Signs and symptoms of the depressive phase of bipolar disorder include (but in no way are limited to): 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.[5]
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Now I can't help but think I have those symptoms at times, but then, don't we all? Surely every one of us have experienced these feelings?