Bipolar II Disorder is defined by the presence of a Major Depressive Episode and at least one Hypomanic Episode (a distinct period of elevated., expansive, or irritable mood lasting, at least, 4 days)  The criteria for a Hypomanic Episode are as follows and include at least three of the following:
 
• Inflated self-esteem or grandiosity
• Decreased need for sleep
• More talkative and/or pressure to keep talking
• Flight of ideas or racing thoughts
• Distractibility
• Increase in goal directed activity
• Excessive involvement in pleasurable activities with a significant potential for negative consequences

A Hypomanic Episode is not severe enough to cause major impairment in social or occupational functioning.

American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fourth  Edition, text Revision. Washington, DC American Psychiatric Association, 2000.