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.Individuals in a hypomanic state have a decreased need for sleep, are extremely outgoing and competitive, have a great deal of energy and are otherwise often fully functioning (unlike full mania).

Specifically, hypomania is distinguished from mania by the absence of psychotic symptoms and grandiosity, and by its lesser degree of impact on functioning.

Hypomania is a feature of bipolar II disorder and cyclothymia, but can also occur in schizoaffective disorder. Hypomania is also a feature of bipolar I disorder as it arises in sequential procession as the mood disorder fluctuates between normal mood and mania. Some individuals with bipolar I disorder have hypomanic as well as manic episodes. Hypomania can also occur when moods progress downwards from a manic mood state to a normal mood. Hypomania is sometimes credited with increasing creativity and productive energy.

People who experience hyperthymia, or "chronic hypomania", encounter the same symptoms as hypomania but long-term.