Although...... psychologically speaking...... it could be Dissociative Personality disorder and that is “one” of his personas..... I mean.... he was traumatized sooooo it’s not something to be not considered but I could also just be over psycho-analyzing this character ╮(￣▽￣)╭
Um.. Sexsomnia DOES exist. It's a sub group/form of parasomnia. People usually develop them from abusing sleeping pills. I can say parasomnia is a real thing, I have it and I sometimes sleepwalk/talk to someone while having absolutely no memory of doing so the next day because I was in DEEP sleep.
Being intoxicated doesn't lead you to initiate sex like sexsomnia. It makes you blank, "stupid", drain ALL of your energy out of your body and you have little to no control of your body when the drugs take effect. I don't know who your psychology teacher is but I'm guessing they're majored in psychotherapy instead of psychiatry. I study psychiatry and we do have this in our syllabus because Sexsomnia is a medical condition, not an emotional/mental condition.
Although it only has very little information as this is considered a rare condition and there's not much study on this.
It absolutely does exist, my partner is a lawyer and he's studied cases involving it, and his firm has also worked on a case. It's represented in the legal system as a very real disorder.
Also I've taken psychology courses and psychology teachers don't know shit tbh. It's way too easy to get a psychology and teaching degree and even at the university level it's often taught by people who know very little in the grand scheme of things.
Psychology as a subject is just extremely broad. You won't cover every single aspect of it unless you specialise and it sounds like sexomnia is a rare and specific disorder that not many would know about.
I know this is fiction but just so no one gets confused.... sexsomnia or whatever thing that Chamin has.... it ain’t real. I looked it up, doesn’t seem to be plausible. I even asked my psychology teacher to be sure and he was like “da fuck? That shit ain’t real. There’s no psychological possibility of something like that to happen and a scenario like that would only occur if you’re on drugs or intoxicated.” Soooooo I’m not saying Chamin could be faking it since it is a fictional story so it could be a real thing in the world of this BL but..... who knows~~~~ I’m not going to make that judgement yet