Second, although there is often a loss of energy and interest, many affected persons also experience a fair amount of agitation, like a sense of being keyed up, antsy, or fidgety. This is reflected in awakening early in the morning and being unable to fall asleep again, even though feeling very tired. It is possible a result of disturbance in circadian rhythms that is often found in depression. The first episode of Major Depression can occur as early as childhood to as late as old age. However, the most common age for first episodes is probably in the late 30's to early 40's.
Women are about three times more likely to experience Major Depression than men.
All social classes are affected, and stress is often a factor. There is clearly a genetic component of moderate importance, with elevated incidence in affected families. Also of note, mood disorders, including Major Depression, tend to be cyclical. Persons who experience one episode have increased likelihood of additional episodes. The average number of episodes is about two, but five or six is not uncommon.