While it's true that during some sleep stages our brains pay very little attention to what's happening around us, during other stages we're able to hear and process sounds even in our sleep. Not only that, but we are listening for certain sounds while we sleep, even when we're in deep sleep.
It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up.
Traditionally, dreamless sleep has been straightforwardly defined as the part of sleep that occurs you're not dreaming, and it has been looked at as one uniform stage. Rather, research shows that people have conscious experiences during all states of sleep, including deep sleep, Thompson told Live Science.
During deep sleep, your body releases growth hormone and works to build and repair muscles, bones, and tissue, and immune system functioning. Additionally, slow-wave sleep may be important for regulating glucose metabolism.
During sleep, our body can decide to ignore sounds, movements and smells happening around us which might otherwise wake us. This decision-making mostly happens in our brain.
If you think you're seeing — or smelling, hearing, tasting, or feeling — things when you're asleep, you may not be dreaming. It's possible that you're experiencing hypnagogic hallucinations. It's more likely if you're waking up in extreme fear that your hallucination was real.
How much deep sleep should you get? In healthy adults, about 13 to 23 percent of your sleep is deep sleep. So if you sleep for 8 hours a night, that's roughly 62 to 110 minutes. However, as you get older you require less deep sleep.
Stage 3 / N3
Stage 3 sleep is also known as deep sleep, and it is harder to wake someone up if they are in this phase. Muscle tone, pulse, and breathing rate decrease in N3 sleep as the body relaxes even further. The brain activity during this period has an identifiable pattern of what are known as delta waves.
Hypersomnia is what doctors call a variety of conditions in which you often feel overly tired or sleep too much. It can happen because of illnesses like epilepsy or Parkinson's disease, or mental conditions like depression. It's also the main symptom of narcolepsy and of a condition called Kleine-Levin syndrome.
During deep sleep, you pay less attention to the outside world. But while you may be out like a light, some parts of your body are hard at work. Your breathing and heart rate go down, but your ability to fight germs and to form memories goes up. Experts are still figuring out exactly what deep sleep is for.
But “in terms of tracking light, deep, and REM sleep, basically all of the devices performed at only a medium level of accuracy,” says Chinoy. Translation: There's only about a 50-percent chance your data is accurate.
Scientists identified a gene that causes people to naturally sleep less than six and a half hours each night without any apparent ill effects. The findings reveal a mechanism affecting quality sleep and suggest an avenue to investigate for new sleep treatments.
This is also the stage of sleep where it is most difficult to wake you up. Deep sleep is as important, if not more important, than REM sleep when it comes to physical rest, so keep an eye on this stage if you're tracking your sleep patterns.
Most adults, but not all, require 7 – 9 hours of sleep. Deep sleep must be a part of this nightly sleep. If you do not routinely get enough deep sleep, a number of issues can arise or be exacerbated including heart disease, a weakened immune system, an increased risk of stroke, and (for men) erectile dysfunction.
Adults generally average 1-2 hours of deep sleep per night, somewhere between 15 and 25% of your nightly sleep. Most of our deep sleep comes in the first sleep cycle of the night, usually 45-90 minutes.
Tactile Hallucinations
Tactile hallucination is the experience of feeling like you're being touched when you're not. It's one of the most common aspects of sleep paralysis. Many people say they feel pressure or contact. It's like something or someone is holding them down.
Although some theorists have suggested that pain sensations cannot be part of the dreaming world, research has shown that pain sensations occur in about 1% of the dreams in healthy persons and in about 30% of patients with acute, severe pain.
The answer is yes, our minds can sense someone staring at us even when we cannot see it/him/her or are asleep. The explanation for this is that our minds are constantly receiving and processing information from our environment, even when we are not consciously aware of it.
The most important sleep stage is Stage 3, Non-REM or, Delta (Slow Wave) Sleep, it takes up 25% of our total sleep cycle, and it's known as the 'deepest' period of sleep. It's in Stage 3 that sleep is at its most restorative, helping our bodies heal themselves and our minds rest.
Sleep without dreams is the most restful sleep. Scratching your head at the last one? No one would blame you. There's no shortage of science-backed tips for better sleep, and about one in five people now use an app or wearable to track and improve their zzz's.
The takeaway.
Spending around 90 minutes in REM sleep each night is considered healthy for most adults, though it depends on the person.
Fu says researchers have found that short sleepers tend to be more optimistic, more energetic and better multitaskers. They also have a higher pain threshold, don't suffer from jet lag and some researchers believe they may even live longer.
Regardless of their preferred mode, bats, elephants, frogs, honeybees, humans and more have something in common: They all sleep. In fact, scientists have yet to find a truly sleepless creature.
According to VietNamNet, TV channels with modern devices have kept track of Thai Ngoc for a long time and they all record that Ngoc has not slept. Thai Ngoc said the insomnia began when he was 20 years old and ten years later he became sleepless.
The only time consciousness fades naturally in a healthy individuals is during deep (dreamless) sleep; this is shown by the frequent inability to recall any mental activity following awakening from this phase (Tononi, 2008).