lol you got that wrong
I think it's too early to say it's catatonia. Dohyun's feeling depressed and doesn't want to respond to Sungho or drink water. It's probably only been several minutes.
I mean that in the comic it only seems to have only been several minutes that he's unresponsive. He's thinking depressed thoughts, he gets untied, Sungho tries to make him drink water and he turns away/faints. Considering Dohyun's thoughts about there being no point in fighting back, I think it could be that he doesn't want to interact with Sungho and he doesn't want water or food because he feels like he'd be better off dead.
Definitely if he carries on not interacting or moving or talking for a longer period of time in season 3 then it could be catatonia but so far I think it's still too early to say.
Did you also learn if there is a chance to return to a stable psychological sstate from the condition, Catatonia, you talked about? I can see Dohyun went through horrible horrible experience so I am not surprised he would shut himself down but still...I do not wish to see him turn into an empty shell. It makes me too sad( つ.σ ).

I studied Duhyun case in Psychology.
It is called Catatonia.
When someone can't indure a harsh incident, the brain decides to go back in time when he was happy.
But if the entire life wasn't happy like Duhyun's
The brain goes to the point where he doesn't excist and the person feels like a corpse or a log of wood which doesn't feel or think or any thing to end that suffering .