Connectivity between viral infections and sleep. Sleep disorders that are caused by parasites include increased duration of slow sleep wave (SWS), periods of wakefulness, and a decrease in rapid eye movement sleep (REM), as well as, in general, sleep efficiency. Other disorders comprise alterations in electroencephalographic characteristics, such as reductions in sleep-spindle and K-complex densities. These changes may be caused by activation of the immune system and the consequent production of cytokines that have various effects on CNS structures, modulating the form and quantity of sleep. Such pathogens can disrupt sleep indirectly, causing respiratory dysfunction, obsessive-compulsive disorder, and mutism, all leading to sleep disturbances, such as sleep apnea-hypopnea syndrome, that accompany psychiatric disorders.