During sleep, our body and brain go through several stages, from falling asleep to waking up. Sleep is not a straight path; instead, it is divided into different cycles. Over the course of a night, we typically experience 4 to 6 consecutive cycles, each composed of four main stages: falling asleep, light sleep, deep sleep, and REM sleep.
On average, a sleep cycle lasts about 90 minutes and follows this order: falling asleep, light sleep, deep sleep, light sleep (again), and REM sleep. However, cycles evolve throughout the night. The first half is rich in deep sleep, while the second half consists mainly of light and REM sleep.
Falling Asleep
This is the first phase, also known as stage 1. Since it leads to sleep, it is crucial that it occurs in the best conditions possible. During this stage, we may feel semi-conscious as our thoughts wander. Breathing and heart rate slow down, muscles relax, and the eyes move beneath the eyelids. As this is a very light sleep state, we can be easily awakened and may experience a sensation of falling or jerking awake.
Light Sleep
After just a few minutes, we typically enter the second stage of the cycle. This phase gradually lengthens throughout the night and makes up about 50% of total sleep. Although drowsiness deepens, we can still wake up relatively easily. Muscle tone remains, allowing movement such as turning over, but there are no longer any eye movements.
Deep Sleep
Representing the third stage of the cycle, this is when we sleep most soundly. Deep sleep is more prevalent in the earlier cycles and accounts for 20 to 25% of total sleep. During this stage, the brain is less responsive to external stimuli like noise and light, making waking up less likely. This phase is crucial for physical recovery, as the body restores energy. The metabolism slows, blood pressure drops, muscles fully relax, eye movements cease, and heart rate decreases.
REM Sleep
The final stage of a cycle is REM (rapid eye movement) sleep, accounting for about 20% of total sleep time. This is when dreaming occurs most frequently. At this stage, the body is completely relaxed and immobile, but brain activity is high, and eye movements are rapid. Breathing and heart rate may fluctuate depending on the dream. Unlike deep sleep, REM sleep lengthens as the night progresses. At the end of this stage, brain activity slows down again, and a new cycle begins.
People with sleep apnea often experience disruptions or even a complete absence of some of these stages. Since sleep apnea causes brain micro-awakenings (brief moments of wakefulness that the person may not be fully aware of), some individuals never reach deep or REM sleep. However, these stages are crucial for both physical and mental recovery, and their absence can lead to fatigue and excessive daytime sleepiness. This highlights the importance of getting quality sleep.
For more information or any questions, feel free to contact us at info@csrsommets.ca or 1-877-744-0416.
