Advanced Sleep Phase Disorder (ASPD) is the opposite of DSPD. It is characterized by habitually early sleep-onset and wake times, compared with societal or preferred norms. The official term for the disorder is: “circadian rhythm sleep disorder, advanced sleep phase type.”
When allowed to choose their preferred sleep schedule, patients with ASPD exhibit sleep of normal quality and duration for their age and maintain a stable (but advanced) relationship of entrainment to the 24-hour, sleep-wake pattern.
Fig. 5.2 Advanced and delayed sleep phase
25. Reid KJ and Zee PC. “Circadian disorders of the sleep-wake cycle,” in Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, 2011, pages 470-482.