There are two basic types of sleep, rapid eye movement—REM sleep, and non-rapid eye movement—NREM sleep.
NREM sleep is the deep sleep cycle and REM sleep is the active sleep cycle. Sleep occurs in a series of recurring sleep stages and each stage varies according to what is happening in the brain and body. Each stage of sleep is vital with each playing a different part in preparation for the day ahead.
Non-REM sleep includes the following 4 stages:
Stage 1 (Transition to sleep) – This lasts about five minutes. The eyes move slowly under the eyelids, muscle activity slows down, and it is easy to be awakened.
Stage 2 (Light sleep) – This is the first stage of true sleep, lasting from 10 to 25 minutes. Eye movement stops, heart rate slows, and body temperature decreases.
Stage 3 (Deep sleep) – You are difficult to awaken, and if you are, you do not adjust immediately and often feel groggy and disoriented for several minutes.
Stage 4 (More intense deep sleep) – This is the deepest stage of sleep. Brain waves are extremely slow. Blood flow is directed away from the brain and towards the muscles, restoring physical energy.
REM sleep occurs about 70 to 90 minutes after falling asleep and is the stage where dreaming occurs. Eyes move rapidly, breathing is shallow and the heart rate and blood pressure increase.
The amount of time spent in each stage of sleep changes as the night progresses. For example, most deep sleep occurs in the first half of the night. Later in the night, the REM sleep stages become longer, alternating with light Stage 2 sleep.
Deep sleep, especially Stages 3 and 4, is a time when the body repairs itself and builds up energy for the day ahead. It plays a major role in maintaining health, stimulating growth and development, repairing muscles and tissues, and boosting the immune system. In order to wake up energized and refreshed, getting quality deep sleep is vital. Factors that can affect deep sleep are: being awakened during the night regardless of the reason, working night or swing shifts, and smoking or drinking in the evening.
Just as deep sleep renews the body, REM sleep renews the mind. REM sleep plays a key role in learning and memory. During REM sleep, the brain consolidates and processes information learned during the day, strengthens memory, and replenishes its supply of chemicals such as serotonin and dopamine that boost the mood during the day.
REM sleep in adult humans typically occupies 20–25 percent of total sleep with the amount of REM sleep varying considerably with age. A newborn baby spends more than 80 percent of total sleep time in REM sleep. During a normal night, about four or five periods of REM sleep is usually experienced. These periods are quite short at the beginning of the night and longer toward the end.
Being deprived of adequate deep sleep, the body will try to make it up first, at the expense of REM sleep. Furthermore, studies have shown that when sleep is deprived, the body becomes “more efficient” at sleep and moves to Stage 3 and REM sleep faster than patients who are not sleep deprived. This allows more time in the critical sleep of Stages 3, 4 and REM sleep.
The effects of sleep deprivation are serious and affect both the body and mind. The most damaging effects of sleep deprivation are from inadequate deep sleep with inadequate REM sleep mostly affecting mood and social interactions. Effects of this varies from irritability, tiredness, social ineptness, “cracking” under stress, memory loss, bad concentration, strange appetite change (always hungry, never hungry), and increased risk of occupational or vehicle injury. Many medical diseases are associated with chronic, longterm sleep deprivation. These include high blood pressure, frequent infections, activity intolerance, heart attack, heart failure, stroke, obesity, attention deficit disorder, and behavioral and social problems.
Knowing that these serious symptoms can result from sleep deprivation and especially chronic, long term sleep deprivation, doesn’t it make sense that we should make time in our busy schedules for adequate sleep? If we make time to sleep, and are right with the Lord, we can claim the promises of Scripture: “I will both lay me down in peace, and sleep: for thou, Lord, only makest me dwell in safety.” Psalm 4:8. “When thou liest down, thou shalt not be afraid: yea, thou shalt lie down, and thy sleep shall be sweet.” Proverbs 3:24.