A series of three dreams occurring over a ten-day period was the prelude to clinical mania. I explain the sudden suppression of depressive affect in the first dream as based on a sudden deepening of sleep and as the start of the manic process. The patient went in ten days from depression to mania, passing through a stage of depersonalization manifested both clinically and in the state of sleep during dreaming. Evidence suggested that there is a nighttime state of sleep corresponding to mania as well as to depersonalization. The state of sleep corresponding to mania is based on a regressive movement within the dreams into a deeper stage of sleep, whereas in depersonalization dreams occur in a somewhat lighter stage of sleep. Repetitive dreaming plays a part in promoting the deeper sleep.