Just my thoughts

Okay so I think he really has illness. Like he developed it after being locked up.

Okay he was 13 y/o when his father said something is wrong with him. Then he locked him up. I think that is when where Seungho lost it and actually become ill. Imagine being locked up because they decided that your sexuality is a disease.

So maybe here is what happened

Losing sleep is actually a very dangerous thing. It causes you a lot of troubles. One common reason of losing sleep is anxiety.
He maybe developed this anxiety over the time he is being "cured". We don't know what kind of methods his father did just to cure him.
Another thing I don't know if you observed but everything that is not going according to his plan is making him lose sleep. He gets cranky.

Maybe that is why he is taking medication so he could sleep. Maybe there is just too much trauma and stuff going on he couldn't sleep. Maybe he just lost it because of this kind of situation where being gay is a disease.

All we know is that he lives in a different time. It is very different from our time. And in my opinion in this country they are more closed to the idea of being gay. So their treatment to those who's sexuality is different from them is often harsh.

Just my thoughts...