What Is Deep Sleep and How To Get It?

A classification process is used to describe the different stages of sleep people go through. Deep sleep is stage 3 sleep or stages 3 and 4 under the classification that includes a stage 4. On an EEG, the voltage difference patterns over time show up as delta waves. Therefore, deep sleep is also described as slow-wave sleep distinguishing it from the fast wave sleep of Stage 2.

Deep sleep is also called heavy sleep because it is more difficult to awaken sleepers in this stage as opposed to light sleep. Additionally, if one is woken up suddenly while in this stage of deep or heavy sleep, they get sleep inertia (extreme drowsiness and disorientation).

People that experience deep sleep are, also, less likely to awaken to external stimuli than those sleepers in light sleep. Deep sleepers move their bodies less than those in light sleep, as well; but more than those in REM sleep.

Your body needs this kind of sleep. It is a time of accelerated tissue repair and body rejuvenation with human growth hormone being released in the first deep sleep cycle of the night. In children, as well, this is a time of physical growth and rejuvenation of the body.

There are also some common sleep disorders that occur in children during this deep sleep stage including night terrors, sleepwalking, and nocturnal enuresis or bedwetting.

Our bodies crave deep sleep more than other types of sleep. If you stay up all night and go about your normal activities the next day, you have some sleep debt. But if allowed to sleep the following night as much as you need to feel refreshed, you will probably not double the time of your normal sleep. Rather, the normal sleep time is appended with an additional one-third to one-half of normal sleep period. So someone who normally sleeps 7 hours per night, may, after a missed night’s sleep, go for 10 hours before feeling back to normal.

The interesting thing is the distribution of time among the stages during this recovery sleep. Pretty much all the lost deep sleep is recovered. The amount of deep sleep during this second night is twice what it is in a normal night. Lengths of REM and light sleep are lower. It seems that the body chooses to conserve slow-wave sleep as much as possible, and it more willing to sacrifice other stages of sleep.

There’s an interesting experiment that shows our body’s desire for deep sleep, even if subconscious.

Scientists monitored the sleep architectures of people with insomnia over an extended period of time. The insomniacs were not given access to their EEG results. The insomniacs were also given access to sleeping pills (benzodiazepines) and told they could take them if they felt they needed to.

After nights when the people had lesser deep sleep, the subjects were more likely to choose to self-administer the sleeping pills. Stage 3 length was the single most important factor in predicting whether pills were taken. This suggests people have a feeling about their need for deep sleep.

How To Get Better Deep Sleep

So, how to get more deep sleep? Deep sleep can be elusive and therefore, there is no certain way to force your brain to spend more time in this stage. All you can do is prepare yourself and hope for the best!

One good way to prepare is to get a full night’s sleep every single night. Sleep medications can help, however, they all change your normal sleep architecture, and none lead to more slow wave or deep sleep. Instead, they increase the time in light sleep which may then lead to deeper sleep.

Strenuous anaerobic exercise, like weight-lifting, may induce more slow-wave sleep but the evidence on this is not firm. Some people react to to exercise better than others when trying to provoke more deep sleep. It is a fact that tissue repair is at its fastest in this stage of sleep as well as the release of the hormone HGH. This can not be overlooked.  

Aerobic exercise, as well, helps some people attain longer deep sleep. Raising one’s body temperature, like soaking in a hot tub, has also been found to increase this type of sleep. So this may be why aerobic exercise has been found to help because it raises body temperature.

The problem, however, with this theory is the fact that people tend to sleep better in cooler temperatures. Stage 3 sleep, or deep sleep does not start until more than an hour after sleep onset during which time the body cools.

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Deep Sleep and Age

Unfortunately, one of the effects of age is the loss of time in deep sleep. In our 20’s we spend 20 percent of the night in this stage of sleep. However, at 40 or 50 we are only spending 10 percent of that time sleeping deeply. Even worse, by age 70 or 80, it is down to less than 5 percent, and sometimes even 2 percent. By looking at a person’s EEG chart for a night, you could easily determine how old they are.

Why is this decline unfortunate? Less deep sleep is not just a result of aging; it appears to at least partially cause some of the negative characteristics of old age. Weakness, decreased mental acuity, infrequent feeling of refreshment in the morning – these are all connected to less deep sleep.

The Difference Between Sound Sleep and Deep Sleep

“Sound” means whole and possessing integrity. Sound sleep is a subjective term given to a night’s sleep that is satisfying to the sleeper. What is considered sound sleep by a 50 year old might be described quite the opposite by a 20 year old.

If we were to hook up a polysomnography machine to a person getting sound sleep, we would see few nighttime awakenings, no significant breathing problems, and a decent amount of time spent in both slow-wave deep sleep and REM sleep.

“Decent amount” is subjective, but we can ballpark it as 90 to 120 min per night of deep sleep and 90 to 130 min per night of REM sleep for adults. (Too much REM is associated with depression. There doesn’t seem to be any such thing as too much deep sleep.)

Sound also somewhat tangentially refers to the depth of sleep and how susceptible the sleeper is to awakening by noise. This concept is probably close to what people mean by sleep deeply.

There are also differences between quiet wakefulness and sleep. One of these is the ability of our brain to react mindfully to external stimuli. The difference between being in a coma and sleep? Sleep is reversible and a coma is permanent. Also, a coma is being in a state where the person can not be awakened by shaking or any external stimuli, unlike someone who is sleeping.

The depth of sleep is generally taken to mean how likely the sleeper is to be awakened from an external stimulus. Children are difficult to awaken not because they are lazy but because they are sleeping deeply.

Even within a single stage of sleep (as measured by EEG) the depth varies as measured by sensitivity to acoustic stimuli. It has also been shown that people who have more “sleep spindles” on the EEG readings during a normal night of sleep have more tolerance for noise.

A hypnogram, which is the output of a polysomnogram is a proven way to show the difference between stages as well. It is typically printed so Stages 3 and 4 ( deep sleep) are shown lower on the page than Stages 1 and 2. This is usually just convention but it further promotes the idea of Stages 3 and 4 being deeper sleep than the earlier stages.

By this measure, some people do sleep deeper than others. Compare two people in stage 3 slow-wave sleep and one may be easier to awaken than the other.

Does this mean the deeper sleeper is getting more of the slow-wave sleep benefits than the lighter sleeper? No. The characteristics and benefits of different stages of sleep are relative to each other, not compared among people. Although some people are lighter or deeper sleepers than others (as measured by susceptibility to awakening), that doesn’t mean they are getting more or less out of sleep.