The normal sleep cycle involves distinct stages from light drowsiness to deep sleep. REM (rapid eye movement) sleep is a different type of sleep, where the eyes move rapidly and vivid dreaming is most common. During a night, there will be several cycles of non-REM and REM sleep.
Many diseases affect sleep and it is increasingly appreciated how sleep has significant effects on diseases themselves. Neurologic disorders that may be particularly important include epilepsy, stroke, dementia, and chronic pain. A variety of pulmonary and cardiovascular diseases are affected by sleep including asthma, thrombotic disease, chronic obstructive pulmonary disease, and cardiovascular disease.