Often in those who have experienced their first episode of hypomania – generally without psychotic features – there may be a long or recent history of depression or a mix of hypomania combined with depression (known as mixed-state) prior to the emergence of manic symptoms. This commonly surfaces in the mid to late teens. Because the teenage years are typically an emotionally charged time of life, it is not unusual for mood swings to be passed off as normal hormonal teen behavior and for a diagnosis of bipolar disorder to be missed until there is evidence of an obvious manic or hypomanic phase.

Hypomania may also occur as a side effect of pharmaceuticals prescribed for conditions or diseases other than psychological states or mood disorders. In those instances, as in cases of drug-induced hypomanic episodes in unipolar depressives, the hypomania can almost invariably be eliminated by lowering medication dosage, withdrawing the drug entirely, or changing to a different medication if discontinuation of treatment is not possible.

Hypomania may also be triggered by the occurrence of a highly exciting event in the patient's situation, such as a substantial financial gain or recognition.

Hypomania can be associated with narcissistic personality disorder.

Mania and hypomania are usually studied together as components of bipolar disorders, and the pathophysiology is usually assumed to be the same. Given that norepinephrine and dopaminergic drugs are capable of triggering hypomania, theories relating to monoamine hyperactivity have been proposed. A theory unifying depression and mania in bipolar individuals proposes that decreased serotonergic regulation of other monoamines can result in either depressive or manic symptoms. Lesions on the right side frontal and temporal lobes have further been associated with mania.