Sleep phases

Our brain activity changes periodically during sleep. Depending on the type of these activities, we can divide sleep into phases that follow one another in a well-defined order, together forming a complete sleep cycle.

REM and NREM

During sleep, our brain 'relaxes' the body, so that most of the time we do not move at all. Those phases during which this happens have been called NREM (non-rapid eye movement) sleep. However, the last phase of sleep is characterised by increased contractions of certain muscles - especially the eye muscles - hence it is called the 'rapid eye movement' (REM ) sleep phase.

Sequence

Phase one is the shallowest phase of NREM sleep, shallow sleep. During it, it is easy to wake up; the eyes may move slowly under the eyelids and the whole body just relaxes. Brain activity slows down. During this phase, you may experience a sensation of falling, which is often followed by a muscle spasm that awakens you from sleep - known as sleep myoclonus. This is a physiological phenomenon that accompanies most people. It does not require treatment.

Phase two is the actual NREM sleep phase. Brain activity decreases further, eye movements subside and body temperature and heart rate decrease slightly. Sleep is deeper and awakening from it more difficult.

The third phase of NREM, deep sleep, is the most important phase of sleep from the point of view of the regeneration of our brain and body, as well as the subjective feeling of being "asleep". People deprived of this phase (awakened at this stage), even when they have slept for an adequate amount of time, feel less rested, and the following day the number and length of third phases increase to compensate for its deficiencies. It is also during this phase that so-called parasomnias, such as sleepwalking, occur.

Some sources also distinguish the fourth phase of NREM sleep, which is an even deeper sleep, also very important for recovery and only occurring during the first cycles in very tired people. The last phase of sleep is REM sleep.

As mentioned earlier, rapid eye movements occur during this phase, and the most vivid dreams occur, which are usually remembered upon awakening. Waking up during this phase of sleep can make us feel tired and disoriented.

Immediately after the REM sleep phase, we 'return to the beginning of the cycle' - to phase one of NREM sleep - and the whole thing starts again. The whole cycle lasts about 1.5 hours for most people. Therefore, it is worth planning your sleep so that its length is a multiple of this time - so that you wake up after the REM phase, being and feeling rested.