Some investigators argue that this finding represents a genetic phenomenon, while others point out a correlation with the widespread use of illicit drugs in the general population. Those who support this position suggest such drug use could account for the early appearance of manic-depressive illness in vulnerable individuals who otherwise would have experienced the onset of their condition a decade later. Changes occur in the person's mood, thinking and behavior. Irritability and anger without provocation are common during an episode of mania. There may be shifts from euphoria, when the individual is gregarious, joking and laughing inappropriately, to irritability or depression.
Moods can change within minutes and in some cases shift constantly from one to another.
During periods of mania, there is an increased sense of physical energy, and the individual may exhibit constant activity. Speech tends to be so fast that other people are unable to interrupt. The flow of the conversation may have no logic, shifting from one topic to the next. The individual has a decreased need for sleep, sometimes not sleeping for days. There may also be changes in sexual behavior.