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Your internal 24-hour sleep-wake cycle, otherwise known as your biological clock or circadian rhythm, is regulated by processes in the brain that respond to how long you’ve been awake and the changes between light and dark.

Hormones that Determine Sleep Patterns

At night, your body responds to the loss of daylight by producing melatonin, a hormone that makes you sleepy. As the sun goes down the pineal gland senses the loss of light and begins to produce the hormone melatonin.

Melatonin creates a sensation of sleepiness and also drops the basal body temperature, signaling the body that it is time to go to sleep. Melatonin production insets by about 9:00 pm.

During the day, sunlight triggers the brain to inhibit melatonin production so you feel awake and alert. Melatonin production stops about 7:00 am.

If your internal clock is disrupted with things such as artificial lighting and shift work deep sleep and sleep cycles may become effected.

Things that ‘Break’ the Sleep Cycle

Your internal clock can be disrupted by factors such as nightshift work, traveling across time zones, caffeine or irregular sleeping patterns (restless leg syndrome, sleep apnea and snoring)—leaving you feeling foggy brained, disoriented, and sleepy at inconvenient times.

The production of melatonin can also be thrown off when you’re deprived of sunlight during the day or exposed to too much artificial light at night—especially the light from electronic devices, including TVs, computers, and mobile phones.

It is important to remove these devices from visibility in the room you sleep in. Even if your eyes are closed, the light from these devices can still be detected.

In chronic day time sleepiness it is important to evaluate not only medical conditions that disrupt sleep (sleep apnea, restless legs, paroxysysmal nocturnal dyspnea and snoring), but also lifestyle habits such as too much caffeine, stimulants, sugar and over exposure to artificial light.

What Really Happens When You Sleep

You may think that once you go to bed, you soon fall into a deep sleep that lasts for most of the night, progressing back into light sleep in the morning when it’s time to wake up. In reality, the sleep cycle is a lot more complicated.

During the night, your sleep follows a predictable pattern, moving back and forth between deep restorative sleep (deep sleep) and more alert stages and dreaming (REM sleep).

Together, the stages of REM and non-REM sleep form a complete sleep cycle. Each cycle typically lasts about 90 minutes and repeats four to six times over the course of a night.

The amount of time you spend 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, your REM sleep stages become longer, alternating with light Stage N2 sleep.

This is why if you are sensitive to waking up in the middle of the night, it is probably in the early morning hours, not immediately after going to bed.

Two Types of Sleep

REM (Rapid Eye Movement)

REM sleep is when you do most of your dreaming. You enter this stage about 70-90 minutes after you fall asleep. Your eyes move in rapid motion and your breathing becomes shallow.

Non-REM (NREM)

NREM sleep contains three stages. As these stages progress, each stage of sleep reaches a deeper state than the previous.

  1. Stage N1 (transition into sleep) – This stage is short, lasting about 5 minutes.
  2. Stage N2 (light sleep) – The first stage of true sleep. This stage lasts about 10-25 minutes. Your heartbeat slows, body temperature drops and eye movement stops.
  3. Stage N3 (deep sleep) – It is difficult to awaken someone in Stage N3. If this stage is disrupted, it often leaves the system feeling foggy, disoriented and delayed. This can last for several minutes in some and an hour or more in others. In this stage of sleep, the brain waves are extremely slow. Blood flow is directed towards the muscular system and away from the brain.

Now you can see that it is important to dedicate plenty of time to sleep. A sleep cycle takes between 70-90 minutes. If you rest 8 hour a night you go through about 5-6 cycles if you get good rest.

If you are tired during the day, adjust your lifestyle accordingly and if necessary be evaluated medically.