Responses
Well, I think the point is to let us see how scary it is that our brains are run by electric signals and how (potentially) easy it could be to mess with. It wasn't really conveyed well (but it could've been!), so sensei had to resort to text at the end (to "explain"). Just my two cents!
So, the whole point of this manga is a basically...nothing. Or is it? lol I'm going to take a crack at making sense of this:
1) The drawers were haunted and when Rin opened them he basically cursed everyone with insanity or false memories or something. I'm not sure how that would explain his dad, though, as his dad wasn't there with them. Unless, it was Himeko and Yama imagining Rin's dad saying those things and praying to Himeko. Basically, everything shown is a mindf*ck based on the premise of "is this really happening" and "what's real". Like I said, insanity.
2) The drawers are cursed or possessed by an entity and whoever comes into contact with the drawers remember the entity as a different person. Again, this doesn't really explain Rin's dad nor does it explain the bit with the teacher or why the other student could see what was happening.
3) Sakiko is a ghost messing with everyone. Again, doesn't explain the dad.
4) Sakiko is really Rin's mom and is haunting them/messing with them and driving everyone crazy. This would explain the dad, but wouldn't explain the drawers out in the middle of no where. Unless the drawers are just a red herring and everyone was crazy before they found them. Sakiko may also be messing with Rin (and the others, by extension) out of revenge for her death, blaming Rin for her death. This could explain why the dad is exempt from the madness but doesn't really explain the last page.
My guess is #1. I think the whole point of this manga is to mess with our heads and question what really happened and what's going on. And that's it. It's probably best not to think too much about it. Your brain will symbolically explode like Rin's.