A restful deep sleep is something we all appreciate and something too many adults cannot achieve with regularity. Ah, sweet slumber, if we only knew you well. Sleep is regarded as restful, healthful and a reliever of stress accumulated during waking hours. Although this is all true, it doesn’t mean there isn’t a lot of brain activity when we sleep. There is, and it can be measured and analyzed with an electroencephalograph (EEG). This activity changes throughout the four basic sleep stages.

Researchers tell us that a healthful night’s sleep is comprised of multiple cycles— each comprised of four stages and lasting an average of 90 to 110 minutes. Obviously, the widely recommended eight hours of sleep may necessitate repeating these cycles and their respective stages four to five times. These stages include shorter transition stages of varying lengths between light and deep sleep.

What are the four stages of sleep?

A general definition is that the first three stages are light to heavy sleep and their transition phases, including wakefulness, with the final stage before awakening, known as REM or rapid eye movement, or active sleep where dreams are most likely to occur.

—Non-Rapid Eye Movement (NREM) Stage 1—

This is the lightest stage of NREM sleep and the slowing of the brain from wakefulness to sleep, with slow-moving eye rolls.  Since it is transitory, it might be described as dozing or drowsy sleep, where disruptions may bring you more quickly to awakening than other stages. Body functions, including brain activity, slow and muscles relax, and you may drift between sleep and wakefulness.

—NREM Stage 2—

Now you are sleeping deeper but not necessarily deeply with less chance of waking up due to outside stimuli. Even though brain waves continue to slow, with sporadic rapid, rhythmic activity that researchers believe assist the brain in maintaining this level of sleep. When we sleep overnight, we are likely in Stage 2 about half of the time with regular breathing and heart rate patterns.

—NREM Stage 3—

This is deep NREM sleep, the most restorative and restful of the stages. Brain activity is marked by delta waves, the slowest rate. You might talk in your sleep and never be aware of it. It is also the domain of sleepwalking and night terrors, feelings of intense fear often accompanied by physical movement or flailing. You are less likely to wake up unless you are physically roused.

—REM Stage—

REM sleep, also known as rapid eye movement, is most commonly known as the dreaming stage.  Along with the rapid side-to-side movement of the eyes, brain activity, and breathing rate increase. You are nearing wakefulness and eye movements are rapid, moving from side to side and brain waves are more active than in Stages 2 & 3 of sleep. You will eventually awaken on your own accord, but if roused during this stage you may feel groggy with a desire to go back to sleep.

Note: The body enters stage 1 while sleeping, followed by stages 2 and 3. After this, stage 2 is repeated before entering the REM sleep stage. After this, stage 2 is repeated again and this entire cycle repeats about 4 to 5 times during the night.


When Are the Best Hours to Sleep?

Your circadian rhythm is your own sleep cycle, affecting your optimal hours to sleep, and it is influenced by external or environmental factors. Daylight, darkness, temperatures and quietude are huge factors for the release of melatonin hormones that make you sleepy. For most of us, due to the previously cited factors and the need for seven to nine hours of sleep, the best time to go to sleep is between 8 p.m. and midnight.

To Nap or Not to Nap?

It is no accident that we call them power naps, lasting 20 to 30 minutes, because they help increase alertness and improve performance. It might even put you in a better mood for the rest of the day. If you’ve been sleeping well at night, keep those naps short or they could be counterproductive.