January 19th my father fell. Since then he's been in the hospital/rehab. Now he's sleeping a lot and not eating. What to do?

I don't think you or they mean assisted living. It sounds as though he needs skilled nursing. Please try to see that he is being rotated in the bed to avoid a bedsore.

You don't mention your father's age. As hard as it may be accept perhaps he does not wish to continue living. Perhaps he just wants the suffering to end. I hope you can speak with staff and access the situation. He is not in any condition for assisted living at present. I hope you get clarification and can speak to the right person about his future care.

He needs to be evaluated by a neurologist. Did he have a CT scan at the hospital? Is he in the hospital now or in rehab? If it was my dad and he's in rehab, I would have him evaluated elsewhere.

Michele what are the doctors telling you? Have you asked them about dads decline? Is your dad working with a neurologist?
Will he eat if you encourage him? Have you brought him something he really likes? Ice cream or a milk shake has lots of calories and you might be able to tempt him with that.
Has he lost weight?
Perhaps the light and noise disturb him and he wants to rest.
Do you think he could be tired from the therapy?
Normally to go into ALF he would need to be able to take care of himself to a degree. How you describe his condition sounds more like a nursing home is needed, unless you are catching him at a bad time. Try to talk to his care team and find out what is going on with him. He might need to be treated for depression.

You need him to be seen by the doctor. It's hard to know what's going on without a doctor checking him out and perhaps doing some tests to see what's going on and why he's so sensitive to light.