Bipolar disorder: A mental disorder characterized by alternating episodes of mania (elevated mood, increased energy) and depression (low mood, decreased energy).
Rapid cycling: A subtype of bipolar disorder where individuals experience at least four mood episodes within a year, with frequent shifts between manic and depressive states.
Seasonal affective disorder (SAD): A type of depression that occurs during certain seasons, usually winter, and is characterized by recurring episodes of depression followed by periods of remission.