system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are you at risk of slipping into a coma after a serious concussion if you sleep for to many consecutive hours?

A friend of mine has to wake up every two hours during the night or he's at risk of slipping into a coma after a serious concussion.
gpt
If you suffer from a concussion, you are at risk for a slow bleed inside your skull that will eventually build up pressure and cause a coma (and/or death.) Most people who have had an injury just want to lay down and rest, but a sleeping person with a worsening brain injury doesn't look or act any different from a sleeping person without: they just look asleep! You wake up the patient every two hours to check their mental status. If the patient is getting harder to wake up or experiencing confusion or other symptoms, they may need surgical intervention...basically a small hole drilled in the skull to relieve the pressure. 

Tl;dr: You are waking them up to check for brain damage, not to keep it from happening.