Just a curious thought I have had. When people enter a coma, since they are still alive they should have some brain activity going on, right? If they have no external stimulus then it shouldn’t those thoughts manifest themselves as dreams? I know they probably don’t have REM in a coma, but I heard that its still possible for normal people to have non-REM dreams so shouldn’t they too? Its just interesting to think that some people could be out for months or possibly years lost in an eternal dreamland. 
…and what if they became lucid? If you can have dreams during non-REM, why not lucid ones.
It’s hard to know exactly what people in a coma experience, because if they experienced nothing it would be very difficult for them to say it. When your friends and family and all of your loved ones visit you daily in the hospital, reading you stories, talking with you, etc., wouldn’t it be impossible for you to say “sorry, I had no idea. You were wasting your time.”?
I dont really know but my guess would be that it depends why they actually are in a coma.What kind of brain damage they suffer from.Then every case would be different and some people could experience dreams or images.
Yes in some case they do dream, but not all the time. The factor of how they got in coma also depends on if they dream or not (like Jack mentioned). If they’re brain-dead, then that’s for sure… they don’t dream, but if they are in coma other than some kind of damages to their brains, there are a big possiblitity that they do dream.
I’ve heard some cases where they dream a lot or even go out of body while their body were recovering in coma. I also heard that they ‘wake’ up in their coma body, being aware of the sounds, feeling, etc., but they couldn’t move at all as if they’re in a nasty case of SP.
One thing I know for sure, you don’t dream all the time in coma.
Hope this insight is helpful. 
I got a chance to talk to a man who had gone through many weeks of being in a coma. I asked him about dreaming and he said that he had dreams during surgery about being cut up into little pieces and sent to members of his family. He thinks that this happened when he was in surgery, would make sense
My friend’s friend was in a coma a week ago last friday. He was in this car accident. He’s all good now cause he woke up 4 days later. He said he remebers nothing in the coma which I thought was normal.
I’ve heard stories of people having long, life changing dreams in comas, but no one that ive known personally.