one of the four temperamental types established by Galen, who believed that the ruddy complexion and cheerful outlook displayed by such individuals was due to the predominance of blood over other body fluids. See humoral theory.
one of four basic types of sleep disorders, differentiated from the other types in that it results from a mismatch between one’s internal circadian rhythm and one’s actual sleep schedule. The equivalent classification in DSM–IV–TR is circadian rhythm sleep disorder (or in DSM–5, circadian rhythm sleep–wake disorder). Rotating work-shift schedules and jet lag are two common causes of this disorder. Diagnosis can involve observation in a sleep laboratory, in which such criteria as nocturnal awakening, sleep time, sleep efficiency, breathing patterns, body temperature, minutes of REM sleep, and sleep latency are measured.