system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Waking up from a coma - why could that person not wake up earlier and what happens to the brain during recovery and at the time of waking up?

EDIT: thank you for all the awesome answers. However, please note that I am still looking for an answer that includes what happens to the mind when you wake up.
gpt
Drug-induced coma can be used to rest the body  or to sedate a person to the point that they can be mechanically ventilated efficiently.  
People can be in coma as a side effect of brain trauma- in which case swelling can cause compression of the frontal lobe (partly responsible for assembling reality) and in bad swelling, the hypothalamus in the brainstem. The hypothalamus is responsible for your level of alertness and the brainstem as a whole isn't fond of being compressed. We can use drugs to reduce swelling in the brain but often mild swelling just needs time to go down and the person can have a varied level of consciousness while they recover.