A late bedtime is actually better than a full night of sleep with interruptions. New study: Adults who had a delayed bedtime experienced only a 12% reduction in positive mood versus 31% in those who were awakened several times during the night. Explanation: The interrupted sleepers had less slow-wave sleep, the type that leaves you feeling restored and rested.

Patrick H. Finan, PhD, assistant professor of psychiatry and behavioral sciences, The Johns Hopkins University School of Medicine, Baltimore.