Self-awakening improves alertness in the morning and during the day after partial sleep deprivation.

The ability to awaken at a predetermined time without an alarm is known as self-awakening. Self-awakening improves morning alertness by eliminating sleep inertia; however, the effects of self-awakening on daytime alertness and alertness that has deteriorated as a result of sleep loss are unknown. The aim of this study was to determine the effects of self-awakening on both morning and daytime alertness after partial sleep deprivation. Fifteen healthy males without the habit of self-awakening participated in a cross-over trial including forced awakening and self-awakening conditions. In each condition, participants' sleep was restricted to 5 h per night in their homes for 4 consecutive days. They completed a psychomotor vigilance task and subjective ratings of sleepiness immediately upon awakening each morning. On the fourth day, participants completed subjective ratings of sleepiness, a psychomotor vigilance task and sleep latency tests in the laboratory seven times at 1-h intervals during the day. The response speed on the psychomotor vigilance task, in the morning and during the day, was higher in the self-awakening than the forced awakening condition. Our results showed that self-awakening improved alertness (assessed by response speeds) by reducing sleep inertia and alleviated daytime sleepiness heightened by partial sleep deprivation.