Seasonal Affective Disorder (SAD) is the form of depression, which is usually caused by an inadequate bright light reaching the biological clock in the suprachiasmatic nucleus. The treatment of this condition involves the application of the light therapy.
Sedatives are the name of chemicals, sometimes of medicines, which are elaborated / or have a tendency to calm and reduce the state of nervousness and / or excitement; in addition, they work by fostering sleep. There are a lot of medicines, which bear the sedative effect. Sometimes some medicines are prescribed for the purpose of calming someone down; however, sedation may also be an undesired side effect of some medicine. Antihistamines, Benzodiazepines, Imidazopyridines, as well as a lot of herbal medicines belong to the most usual sedatives.
Serotonin is the kind of a neurotransmitter, which is involved in several important functions of the body. To these functions belong arousal, emotions, memory, moods and sleep.
Sleep is the name of the natural period suspension of consciousness, during which all powers of the body get restored. Sleep is also characterized by lessened consciousness and slowed – down metabolic processes.
Sleep Apnea is the name of a condition, when the sleeping person stops breathing repeatedly for 10 or even more seconds during his or her sleep. There exist three main types of sleep apnea: obstructive, which is the most widespread, central and mixed. This health condition can be dangerous enough, because people, suffering from sleep apnea, can stop breathing hundreds of times during the night, and these periods of non – breathing can last more than one minute.
Sleep architecture is the general name of NREM and REM stages and cycles of sleep, as well as time of sleep, spent in every stage. As a rule everyone’s sleep architecture gets changed with the age. There is the tendency, observed in middle – aged and in elderly people to spend less time in deeper sleep, in comparison with younger people. Thus, by age 60 – 70 most adults tend to experience some decrease in proportion of time, spent in delta sleep period, though the percentage of REM sleep does not get changed significantly.
Sleep Cycle is the term, which is applied to describe the pattern of stages of sleep, especially the NREM – REM cycle.
Sleep Debt is the name of the psychological condition, which can result from recurrent sleep deprivation, when a person does not receive sufficient restorative daily sleep that is considered to be necessary for the sense of feeling rested and refreshed maintenance.
Sleep Deprivation is the name of a process, by which the requirement for sleep is not met.
Sleep Disorders is the general term, which can be applied to a great variety of illnesses, including abnormalities in psychological functions of the person during sleep, abnormalities of the person’s biological clock, dysfunctional sleep mechanisms, sleep disturbances, which are induced by factors extrinsic to the sleep process.
Sleep Fragmentation is the process or phenomenon of sleep interruption because of the frequent sustained awakenings or because of early morning awakenings.
| 
