Sleep is a behavioural state characterised by little physical activity and almost no awareness of the outside world. We all know when we need to sleep, we can feel this need. We also know when sleep has done its work, we feel rested and full of energy. Another important feature of normal sleep is that it can end quickly. Although a sleeper may appear to be unconscious, a sleeping person can be easily awakened and can resume normal waking activity within a minute or two.
Sleep is an active, highly organised sequence of events and physiological conditions. Sleep is actually made up of two separate and distinctly different states: ‘non-rapid eye movement sleep (NREM sleep) ‘rapid eye movement sleep’ (REM sleep) or dreaming sleep. NREM sleep is further divided into stages 1 – 4 based on the size and speed of the brain waves generated by the sleeper. Stages 3 and 4 of NREM sleep have the biggest and slowest brain waves. These big, slow waves are called delta waves and stages 3 and 4 sleep combined are often called ‘slow-wave sleep’ or ‘delta sleep’. During REM sleep you can watch the sleeper’s eyes move around beneath closed eyelids. We are almost completely paralysed in REM sleep, only the heart, diaphragm, eye muscles and the smooth muscles (such as the muscles of the intestines and blood vessels) are spared from the paralysis of REM sleep.
To identify what stage of sleep one is in, they measure how much noise or other alerting stimulation is required to awaken a sleeper from the various types of sleep. People in stages 3 and 4 sleep require the most stimulation to awaken. Therefore, this phase of sleep is often thought of as ‘deep sleep’. Also, large spurts of growth hormone are secreted during stages 3 and 4 NREM sleep. Consequently, these stages of sleep are thought to restore the body from the wear and tear of waking activity.
A sleep disorder is a medical disorder of the sleep patterns of a person or animal. Some sleep disorders are serious enough to interfere with normal physical, mental, social and emotional functioning. Disruptions in sleep can be caused by a variety of issues, from teeth grinding to night terrors. When a person suffers from difficulty falling asleep and/or staying asleep with no obvious cause, it is referred to as insomnia.
Sleep disorders are broadly classified and can include sleep apnea (stops in breathing during sleep), narcolepsy (excessive sleepiness at inappropriate times), cataplexy (sudden and transient loss of muscle tone while awake), and sleeping sickness (disruption of sleep cycle due to infection). Other disorders include sleepwalking, night terrors and bed wetting. Management of sleep disturbances that are secondary to mental, medical, or substance abuse disorders should focus on the underlying conditions.
