What makes lying awake subjectively so disagreeable to many persons suffering from functional sleep disturbance, in addition to experiencing concomitant vegetative symptoms, is the experience of night and especially darkness as an additional negative factor. This reaction is not restricted to persons having cyclothymic dispostions.

Many persons who react to the night in this manner are by day unusually active, cheerful, and well-adjusted, with no traces of suffering from problems in sleeping or of experiencing night terrors and despondency. Evidently there is a special form of nocturnal depression among persons whose mood varies greatly with light. On sunny days they are irrepressible and in a mood of feeling they can embrace the world, while they almost become depressive during long periods of gray and fog. Paradoxically or typically, they sleep better during the bright, short summer nights than during the long winter nights. This tendency concurs with observations made in Scandinavian countries, especially Lapland, where sleep disturbances are more prevalent and evidently more severe than in comparable countries at other latitudes. Where there is too much interruption in the circadian periodicity and in the normal sleep-wakefulness rhythm, light as an arousal stimulus and darkness as an inducement to sleep therefore seem capable of producing psychic imbalance.

What can be done, though, about such functional sleep disturbances? How is it possible to cope with them without becoming hopelessly dependent on sleeping pills? Let us remember man's biological clock and think of sleep as an instinct-related event that can be learned.

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