Bipolar II disorder occurs relatively infrequently, affecting only approximately one-half of one percent of the population. The majority of such individuals function well between mood episodes (i.e., when they are experiencing neither a major depressive episode nor a hypomanic episode).
As indicated above, hypomania is characterized by a decreased need for sleep - although not insomnia. Major depressive episodes, on the other hand, are characterized by sleep disturbance (often in the form of insomnia). Therefore, individuals with bipolar II disorder would have a high likelihood of periodically experiencing diminished sleep. Also, bipolar II disorder runs in families, with close relatives showing elevated rates of bipolar II disorder, bipolar I disorder, and major depressive disorder. For this reason, family members of those with bipolar II disorder would be expected to have diminished sleep compared with the general population. But, while it is likely that those with bipolar II disorder have family members who sleep less than the rest of us, there is no clear evidence that a family history of chronic insomnia is a specific indicator of bipolar II disorder.