What is Hypomania?

Legal Definition
Hypomania (literally "under mania" or "less than mania") is a mood state characterized by persistent disinhibition and pervasive elevated (euphoric) with or without irritable mood but generally less severe than full mania. Characteristic behaviors are extremely energetic, talkative, and confident commonly exhibited with a flight of creative ideas. While hypomanic behavior often generates productivity and excitement, it can become troublesome if the subject engages in risky or otherwise inadvisable behaviors. When manic episodes are "staged" according to symptomatic severity and associated features, hypomania constitutes the first stage, or stage I, of the syndrome, wherein the cardinal features (euphoria or heightened irritability, pressure of speech and activity, increased energy and decreased need for sleep, and flight of ideas) are most plainly evident.
-- Wikipedia
Legal Definition
A mild or slightly developed form or type of mania
-- Black's Law Dictionary