APG,
It's actually different than rapid-cycling. Mixed episode is when you have both symptoms mannia and depression at the same time.
In the context of bipolar disorder, a mixed state is a condition during which symptoms of mania and clinical depression occur simultaneously (for example, agitation, anxiety, aggressiveness or belligerence, confusion, fatigue, impulsiveness, insomnia, irritability, morbid and/or suicidal ideation, panic, paranoia, persecutory delusions, pressured speech, racing thoughts, restlessness, and rage).
Mixed episodes can be the most volatile of the bipolar states, as moods can easily and quickly be triggered or shifted. Suicide attempts, substance abuse, and self-mutilation may occur during this state.
I hope that was enough information for you. 