system
Given the following post, respond as if you're commenting on Reddit:
human
What are measurable signs of quality sleep?
gpt
Some of the simplest metrics for quantifying sleep quality are:

* The number of awakenings per night.

* The percentage of time in bed spent asleep.

* The total sleep duration obtained.

More detailed metrics can be obtained by studying sleep content, which requires polysomnography (a combination of electrodes that record brain activity, eye movements, and muscle movements). These metrics include:

* The amount of slow-wave activity in the EEG. Slow-wave activity is one of the best markers for sleep need. Slow waves are mostly expressed in the deepest stages of non-REM sleep. The amount of slow-wave activity tails off across the night, and if an individual is sleep deprived they tend to express more slow-wave activity.

* The amounts of time spent in REM sleep and slow-wave sleep (i.e., the deepest stage of non-REM sleep). In an individual with severely disrupted sleep (e.g., due to severe sleep apnea), time spent in these stages is typically decreased.

There can also be signs during the day that an individual is not obtaining sleep of adequate duration or quality. These include:

* Impaired performance on cognitive tasks, the most sensitive being the *psychomotor vigilance test*, which is a serial reaction time test.

* Ability to fall asleep very rapidly during the daytime (as measured using the *multiple sleep latency test*, which is basically a test of how quickly you can fall asleep on demand in a dark room), or in situations where it would not be normal to fall asleep (e.g., while in a car waiting for the lights to change).