Sleep occurs in waves, with a trough called deep sleep when we are in maximum recovery mode. Its nature is somewhat less well known than the more dramatic "dream sleep” during REM. During deep sleep, blood pressure drops, breathing may become slightly slower, and muscles are relaxed as tissue growth and repair occurs and energy is restored. Most deep sleep occurs during the first two sleep cycles of the night, with the greatest amount typically occurring in the first cycle. As the night progresses, deep sleep decreases and is replaced by an increasing amount of REM sleep toward morning.
Deep sleep is effective in decreasing the sleep drive that builds steadily over the course of the day. Short afternoon naps of about 20–25 minutes or less do not allow enough time to cycle into deep sleep, and therefore are less likely to result in the difficulty falling asleep that longer naps can produce.
Our access to deep sleep is vulnerable to the effects of stress, sleep disruption, lack of physical exercise, timing of meals, and caffeine consumption, among other things. Without adequate deep sleep, these factors contribute to the run-down feelings people may frequently experience.
A few suggestions for increasing deep sleep:
- Restrict or eliminate caffeine several hours before bedtime, as it can reduce time spent in deep sleep.
- Bring lavender into your bedroom. The scent has been shown to decrease heart rate and blood pressure, potentially putting you in a more relaxed state, as well as increasing your amount of deep sleep.
- Stress can reduce your ability to get a sufficient amount of deep sleep. Try de-stressing from the day by reading a good book or with some light stretching while listening to relaxing music.
- Avoid spicy meals at dinner; eating a spicy meal before bedtime lessens your time in both light and deep stages of sleep; it can also make falling asleep more difficult.
- Keep your room, bed, and body at a comfortably cool temperature. Temperature can have an even greater effect on your sleep cycle than ambient light.
- Eating a meal high in fiber and low in saturated fat and sugar at least 2–3 hours before bedtime may help you fall asleep faster and increase deep sleep.
- Morning exercise can provide a particular boost to deep sleep and help you sleep more soundly at night. Exposure to a bit of morning sunlight will also help make you feel alert and keep your circadian rhythm on track.