Lately I've been pondering on this a lot but it and debating whether to show it or not. 

Between these rooms Evan's bed is twin sized with only one nightstand in his room. No Closet is seen in front of his bed. No dresser, only one door my guess is there's a window in the middle where the plushies are like Midnight motorist has.

I don't think the fnaf4 bedroom is a hospital room as they wouldn't have toys on the ground a loud ass grandfather clock playing every night at 12 am, and there should be other hospital rooms on each side really, or just the fact that the patient gets up at night and plays with a plush doll for two hours, slamming and opening doors all night.

The reasons I personally think its Mike is

1. The bedrooms
They're way too different and it makes no sense why Fredbear Plush would claim "He locked you in your room." Then Evan remains/is shown in that bedroom as seen above.

I don't think Evan owns two bedrooms so the one with a closet has to be Mike's. The one with a mangle toy is likely either A a guest bedroom that Charlie likely keeps. Or B possibly Elizabeth's room and her parents have split custody with her.

2. The minigames aren't in the current time

They're like past memories that had already happened and are just replaying we see it in fnaf2 ,3, and Sister Location. So fnaf4 is no surprise really. So what we see in the fnaf4 minigames already happened Evan is dead. Same goes to fnaf2 minigames those kids already died the puppet awoke all of them.

3. Mike wouldn't have drawn Nightmare Fredbear in the logbook if he didn't know about him.

4. If the crying child lost his frontal lobe from the bite he wouldn't feel fear so he wouldn't have the nightmares as THOSE form from FEAR. The fact the person in fnaf4 is darting around the entire room all hours screams extremely paranoid to me.

5. The nightmares attack pattern
Personally it doesn't make sense to me on the nightmares represent the bullies. When the bullies didn't seem to be around much. Plus why would they attack in a fnaf1 style for?

They've never been seen running around and hiding under the bed to jump Evan. Only Mike has. If you ask me the nightmares attack pattern matches the fnaf1 style speaking of fnaf1 we do hear fnaf1 phone calls in the background in fnaf4 at times.

Perhaps Mike is like Stanley where he falls asleep on the job in fnaf1 and suffers from the nightmares throughout the night. The dream sequences likely could've started it and the spirits attached themselves onto Mike like Shadow Bonnie did to Toby and cause nightmares/hallucinations.

6. Iv bag, flowers, and pills
I think the pill bottle is likely some sleep drug since Michael likely had a rough time sleeping. Or possibly he has sleep paralysis which makes the nightmare animontronics even worse.
The iv bag my guess is its possible Mike's health started to decline and he neglected to give proper care and going to the doctor regularly. If Mike did land into the hospital I think the flowers came from his mother as I don't see William getting flowers for Mike. His siblings are basically dead at this point on and I don't think he or his friends communicate anymore.

No i'm not saying that the bite of 83 and all didn't happen. Evan simply isn't the one who suffered from the nightmares and the fnaf4 bedroom we play in is Michael's bedroom.

Side of house =👇

Front of house Evan's room and the unseen windows.