What is a defining feature of dyssomnia?

A defining feature of dyssomnia is characterized specifically by abnormalities in the amount, quality, or timing of sleep. This category of sleep disorders encompasses various issues such as insomnia, hypersomnia, and circadian rhythm sleep disorders, which all disrupt normal sleep patterns. Individuals suffering from dyssomnia may experience difficulty falling asleep, staying asleep, or may sleep excessively yet still feel unrested—reflecting significant deviations in sleep that affect overall health and functioning.

In contrast, the other options do not encompass the comprehensive nature of dyssomnia. For instance, decreased total sleep time can occur in certain specific conditions like insomnia, but it doesn't define dyssomnia as a whole since some forms might involve excessive sleep. Regular sleep patterns would indicate a healthy sleep-wake cycle, which contradicts the essence of dyssomnia. Increased quality of REM sleep is not a feature associated with dyssomnias, as these disorders often lead to disturbances that affect REM sleep among other sleep stages.