Although we may think that there are nights when we don't dream, our brain can go through up to 6 stages of sleep in which mental images are produced. Sleep is a physiological process that the body constantly needs to replenish the energies depleted during the day, as well as to perform some internal actions proper to the body and its proper functioning. The stages of sleep are the phases that the process goes through. These stages are vital for a quality sleep without distractions that do not allow the body to rest fully. Sometimes the stages of sleep can be affected by factors outside the body such as : - Tobacco consumption - Excessive coffee consumption - Alcoholism - Anxiety - Stress How can a body that is entering a state of sleep be physiologically recognised? By keeping the eyes closed, the electrical oscillations can be seen clearly on the electroencephalogram (EEG) at an alpha rhythm of 8-13 per second. As the minutes pass, changes associated with each stage of sleep become apparent, depending on the brain's activity. How are the stages of sleep divided? Stage 1 : It belongs to the light sleep stage. It is a short state of drowsiness because it is that stage in which the brain enters and leaves sleep, as well as counting on very easily to wake up. Within stage 1, the eyes have rapid movements, this process is known as REM sleep while the muscles slow down. The person is able to perceive auditory and sensory stimuli, being little or not at all refreshing, as it is a stage of minimal rest. It is also during this stage that sudden muscular contractions occur. This is why we can sometimes notice this sensation of suffering a sudden fall: it is the perception of going deep into stage 1 to move in a few minutes to stage 2 of sleep.