What is "sleep latency" in the context of polysomnography?

Sleep latency refers specifically to the time interval between the moment a person attempts to fall asleep (often marked by the turning off of the lights) and the onset of sleep. This measure is particularly important in polysomnography, as it provides insight into various sleep disorders such as insomnia. A shorter sleep latency may indicate excessive daytime sleepiness or sleep deprivation, while a longer latency could suggest difficulty in initiating sleep, which is a common issue in several sleep disorders. Monitoring sleep latency allows sleep technologists to assess a patient's ability to transition into sleep and identify potential underlying issues affecting sleep quality.

The other options pertain to different aspects of sleep that do not define sleep latency: sleep cycles involve the progression of different sleep stages throughout the night, REM sleep specifically refers to one of those stages characterized by rapid eye movement, and the frequency of awakenings relates to disruptions during sleep rather than the time taken to initially fall asleep.