Wiktionary
n. (context pathology English) A difficulty in falling asleep, or in remaining sleeping
Wikipedia
Dyssomnias are a broad classification of sleeping disorders involving difficulty getting to sleep, remain sleeping, or of excessive sleepiness.
Dyssomnias are primary disorders of initiating or maintaining sleep or of excessive sleepiness and are characterized by a disturbance in the amount, quality, or timing of sleep.
Patients may complain of difficulty getting to sleep or staying asleep, intermittent wakefulness during the night, early morning awakening, or combinations of any of these. Transient episodes are usually of little significance. Stress, caffeine, physical discomfort, daytime napping, and early bedtimes are common factors.