A 31-year-old female presents with a 3-year history of mood instability. She describes recurring periods of 2-3 days of elevated mood, increased energy, decreased need for sleep, and increased talkativeness, alternating with periods of low mood, fatigue, and social withdrawal lasting about a week. During elevated periods she remains functional at work and does not engage in reckless behavior. During low periods she feels sad and tired but continues eating, sleeping, and going to work. She has never had a period longer than 6 weeks without mood fluctuations. Chart review confirms she has never met criteria for a major depressive episode or a hypomanic episode lasting 4 or more consecutive days.