The second type of sleep is REM sleep. This is where the brain is active and the body is inactive. REM sleep typically occurs after about 90 to 120 minutes of non-REM sleep. Most sleep periods will have four to six REM episodes. REM sleep is vital for psychological wellbeing. Those individuals deprived of it typically complain of moodiness and irritability. Since REM sleep is clustered toward the end of the normal seven to eight-hour sleep period, those whose sleep tends to be shorter or fragmented, as in shift workers, are more likely to be REM-deprived.
The traditional shift rotation is a weekly counterclockwise rotation. Recently, it has begun to fall out of favor because medical research has demonstrated that it leaves the biological clock in shambles. Researchers now increasingly recommend clockwise shift rotation with at least a month between rotations to allow for circadian rhythm stabilization.
The Gold Standard circadian rhythm for any industry that requires continuous service has been to work the same shift all the time. Those working shifts exclusively must maintain the same sleep period, even during nights off, to prevent disruption of their biological clocks. Because sunlight is a powerful time-giver, nocturnal training will be lost after two or three days unless this rule is strictly followed. Most police officers resist this concept because it interferes with daytime social and family functions. Unfortunately, resistance also compromises anchor sleep, which minimizes circadian desynchronization.
Anchor sleep is a period of at least four hours during which one sleeps every day while on a particular shift rotation. If you sleep from 8 a.m. to 4 p.m. after working nights, for example, and from 4 a.m. to noon on days off, the overlapping interval from 8 a.m. to noon is called anchor sleep. Sleeping until noon is preferable to sleeping all day for most individuals with families and daytime social commitments. By sleeping through at least half of the time normally reserved for sleep, the circadian rhythms are anchored to a particular schedule and minimally disrupted.
Napping is thought by most investigators to be restorative and useful in promoting alertness during or following night work. Napping before work seems to provide some benefit, and most medical researchers believe it does no harm. If you do nap, allow at least 20 minutes before starting your shift to leave enough time for sleep inertia to dissipate. Power naps of 30 to 45 minutes can be helpful for maintaining alertness. However, napping for longer than one hour can affect the next night's sleep. A longer nap is useful prior to a night shift.