It's commonly used in medical terms related to sleep disorders or abnormal sleep patterns.
Here are some examples:
* Insomnia: Difficulty falling asleep or staying asleep.
* Somnambulism: Sleepwalking.
* Hypersomnia: Excessive sleepiness.
* Narcolepsy: A sleep disorder characterized by uncontrollable sleep attacks.
* Parasomnia: A sleep disorder characterized by abnormal behaviors or physical events during sleep.