Libido is tied to the presence of Testosterone. Throughout the day, it is secreted every 90 minutes but reaches its lowest level in the afternoon. During the night the secretion peaks just prior Rem sleep continues production throughout the Rem periods (Dreaming Sleep). If sleep is interrupted then Testosterone is reduced. Cortisol, the stress hormone, is increased during Sleep Apnea. This hormone in levels reduces the production of Testosterone as well.