Chronic insomnia and daytime functioning: an ambulatory assessment.

In this ambulatory study, the relation between daytime functioning and chronic insomnia was investigated. The study sample consisted of 39 chronic insomniacs and 20 healthy control participants. Performance (vigilance, working memory, motor control) and well-being (concentration, fatigue, mood, sleepiness) were assessed by means of a validated test battery, and intra-individual sleep variability was taken into account. Subjective well-being was found to be compromised in insomniacs as compared to control participants, but no differences in the level of performance were found. Evening cortisol levels did not indicate increased levels of arousal in the insomniacs. Although the absence of an effect of chronic insomnia on objectively measured performance may be due to experimental or statistical factors, this study hypothesizes that the insomniacs studied in the field may have been able to exert compensatory effort to overcome their self-perceived fatigue.