Fatigue and sleep disorders.

Fatigue has often been confused with sleepiness and has received little study as an independent symptom of sleep disturbance. To investigate if fatigue is a common and severe symptom in sleep disordered individuals, the Fatigue Severity Scale (FSS) was administered to 206 patients over a 12-month period at a sleep disorder center. Our sample averaged 4.8 on the 7-point FSS, which is in the severe fatigue range. High fatigue was present in a broad range of sleep disorders, but was particularly high among individuals diagnosed with psychophysiological insomnia. A number of variables predicted fatigue (being female, being a smoker, high BMI, low sleep efficiency percent, and high MMPI average clinical scale score), but surprisingly daytime sleepiness (as measured by the multiple sleep latency test) did not. Apparently, daytime sleepiness and perceived fatigue are independent phenomena. We discussed the importance of attributing credence to the complaint of fatigue and suggested some areas for future study including further study of fatigue in insomnia, expanded consideration of sleep variables causing fatigue, and testing objective measures of fatigue.