Sleep is a state of unconsciousness from the external world, accompanied by a gradual decrease in muscle tone, occurring at regular intervals. Sleep occupies nearly one-third of a human’s life. In individuals without sleep apnea, three to five sleep cycles of approximately 90 minutes each occur during the night, consisting of four distinct phases. The first three phases make up slow-wave sleep, while the fifth stage corresponds to REM (rapid eye movement) sleep, where dreaming occurs.

Stage 1: Drowsiness

This is the stage of falling asleep, marking the transition between wakefulness and sleep. This stage is considered normal when it lasts less than 20 minutes. During this phase, there is a decrease in heart rate, blood pressure, respiration, and body temperature.

Stage 2: Light Sleep

This stage accounts for about 50% of total sleep time during the night. At this stage, individuals are highly sensitive to external stimuli. Muscle tone remains similar to that in Stage 1. Vital signs are stable but slowed.

Stage 3: Transition Phase Between Slow-Wave and Deep Sleep

This phase is very brief and leads into Stage 4.

Stage 4: Dream Stage

This is the stage of dream sleep, where brain activity is very rapid. There is an increase and instability in heart rate and respiration, along with a rise in blood pressure and blood flow. This phase plays a crucial role in learning and memory function.

In summary, sleep is a periodic state of unconsciousness that plays a vital role in our lives. It consists of different stages, including drowsiness, light sleep, the transition to deep sleep, deep sleep, and REM sleep. Each of these stages has specific physiological characteristics, with variations in vital signs, muscle tone, and hormonal activity. Understanding these sleep phases is essential for maintaining good health and ensuring quality rest.

Sleep well!