Sleep Basics

Depending on how long you’ve been struggling with poor sleep, you may have a hard time remembering what it feels like to sleep well or experience normal sleep. However, there really isn’t such a thing as “normal” sleep. There are, however, certain elements that characterize a typical sleep pattern for most healthy adults.

The average healthy adult:

  • Has two to three remembered awakenings per night
  • Has up to 700 “arousals” per night, consisting of very brief awakenings (lasting a few seconds) which are not remembered
  • May take anywhere from 5 to 30 minutes to fall asleep
  • May sleep only about 85 percent of the total time spent in bed at night.

The Stages of Sleep

Have you ever noticed that sometimes your sleep feels deep or light? That’s because not all sleep is the same. Some sleep is deep, some is light, some is intermediate, and some sleep is strongly associated with dream experiences. It’s normal to get all of these types of sleep but in different proportions or stages.

There are four different stages of sleep. These four stages differ in depth, quality, amount, function, and timing of their occurrence during the night:

Stage 1 Sleep:

  • Occurs during the transition from awake to sleep and may last only a couple of minutes
  • Is associated with initial slowing of the brain wave activity
  • Is so light that the sleeper will often report the experience of being “awake” during this period
  • Comprises only about five percent of the night for the typical sleeper

Stage 2 Sleep:

  • Is referred to as the first real stage of sleep; people usually experience this stage as sleep
  • Is when the sleeper stops responding to sounds and other stimuli in the environment
  • Is deeper than stage 1 as it involves further slowing of brain waves. However, it is often experienced as light sleep.
  • Comprises the largest portion of a typical night’s sleep (40-50%)

Stage 3 Sleep:

  • Is also known as delta sleep, slow wave sleep or deep sleep
  • Involves very large and slow brain waves
  • Is most prevalent in the first third of the night
  • Is highly abundant in young children and adolescents
  • Is when growth hormone is released
  • Declines in older age
  • Is strongly associated with the feeling of having been asleep and feeling rested
  • Comprises about 20-25% of the typical night’s sleep

REM Sleep:

  • Is known as “rapid eye movement” sleep or “dream sleep”
  • Is most often associated with vivid dreams
  • Involves highest metabolic brain activity (higher than awake)
  • Is sometimes experienced as wakefulness
  • Is associated with rapid eye movements and muscle paralysis
  • Is most prevalent in the last third of the night
  • Comprises about 20% of a night’s sleep

Sleep “Cycles”

The four sleep stages occur in cycles throughout the night. It typically takes between 90 and 120 minutes to complete one cycle and involves movement through stages 1, 2, 3, and REM. We may go through four to six cycles per night, depending on how long we’re asleep. Brief awakenings at night are natural and usually occur between sleep cycles.

As sleep unfolds across the night, the slow wave sleep episodes become shorter and the REM episodes become longer. As a result, most of our deep sleep occurs early in the sleep period and most REM occurs later.

Sleep Length and Sleep Quality

The continuity of sleep is very important, as it is a key to whether or not you feel rested in the morning. Even if you get a lot of total sleep time, it will be less refreshing if it is highly fragmented, rather than undisturbed. Getting as much of your slow wave sleep as possible will also help you to feel rested, and most slow wave sleep occurs within the first few hours of sleep. Exercising during the day helps to increase slow wave sleep. A key goal of CBTI is to consolidate sleep at night in order to maximize its restorative potential.

Our Biological Need for Sleep

Everyone needs sleep and everyone does sleep – even people with serious insomnia. This is because sleep is essential to life, and your body will try to get it any way it can. The potential to sleep is present, even if there are obstacles preventing optimal sleep.

The purpose of CBTI is to identify these obstacles, and either remove them or alter them, to allow you to sleep as well as you possibly can. One element working in your favor is the biological fact that you need to sleep.

There are two factors that contribute to the biological drive for sleep. The first can be thought of as the need for sleep-wake balance and the other is the sleep-wake circadian rhythm.

Sleep-Wake Balance

Simply put, sleep-wake balance refers to the fact that the longer you go without sleep, the more the need to sleep builds up. One of sleep’s functions is to reverse the effects of wear and tear that wakefulness has on the brain and body. In other words, sleep restores balance. This process is also referred to as sleep homeostasis.

Under normal circumstances (when we are sleeping well) this balance is restored every 24 hours. However with chronic insomnia it may feel like you are in a constant state of imbalance, with too much time awake and not enough time asleep. This feeling is legitimate, but chances are your brain is catching up on sleep either by sneaking in periods of light sleep at night (when you don’t notice) or by giving you one surprisingly good night of sleep every so often.

One of the goals of CBTI is to restore and sustain a normal sleep-wake balance by modifying any problematic sleep wake-behaviors or tendencies that may be disruptive.

Circadian Rhythm

One of the most important factors governing the timing of sleep is the sleep-wake biological rhythm or circadian rhythm. The name “circadian” comes from “circa dia” which is Latin for “about a day”. The sleep-wake rhythm repeats itself about every 24 hours in conjunction with the day-night cycle.

The sleep-wake circadian rhythm is essential to the regulation of healthy sleep for a number of reasons. First, the sleep-wake rhythm is synchronized to the light-dark cycle of day and night. As humans, we are typically awake and active during the light of day and we sleep during the dark of night. Therefore, exposure to light or dark conditions can have a profound impact on the likelihood that we will fall asleep.

Second, there resides within the brain a sleep-wake clock that operates regardless of day and night (light or dark). So, even if we had no idea what time of day or night it was, our brain would still want to go to sleep at roughly the same time every evening and stay asleep for the same amount of time as we would in a normal environment with sunlight cues.

Third, the circadian rhythm is highly susceptible to disruptions and this can lead to insomnia. Such disruptive influences include shift-work and jet lag. When these factors cause insomnia we call it a “circadian rhythm sleep disorder.”

Lastly, if you have chronic insomnia, your circadian rhythm may have adopted a dysfunctional pattern. The circadian rhythm will not correct itself on its own. In order to re-set the circadian rhythm, you need to change your sleep-wake behavior first.

Sleep Topics

Sleep Basics

Children's Sleep

Restless Leg Syndrome


Sleep in Elderly

Womens' Sleep




© Sleep Medicine Website Design | Medical Website Design by Vital Element, Inc.