Yes, as odd as it may sound to some people - despite Khan being who he is, genetically superior on many levels, strong and healthy, having been drilled and shaped from his early childhood on to achieve perfection, possessing blood that heals him (and others) from almost any illness... he actually needs sleep.
It annoys him too, that basic need; If he were allowed to decide what to change about himself, he would ask for said need to be eradicated from his existence. Yet, probably because of his extremely fast metabolism, sleep is a necessity, even if he doesn't need as much as the average human does. Three to four hours are perfectly sufficient for him, and two hours will allow him to keep going for the day - but only for a certain amount of time before exhaustion sets in.
He's barely getting two lately, more on the side of one to two hours, and even though he's not breaking because of it - he can keep going for longer, he's not at his limits yet - Khan can feel the effect it has on him. Muscles feel heaver than usual, his neck and shoulders are tense, and the steady hum of something akin to a headache sits within the back of his head at all times. It's easy to ignore for now, but at some point it won't be anymore.
"---Didn't know a Vulcan meld could do that - render someone unconscious.", is what he gives as an answer to the Vulcan's offer; Khan's not highly educated when it comes to Vulcans, so he only knows the basics regarding their kind, including the fact that they can initiate mind-melds that will... do things. More or less pleasant, depending on the situation one is in.
It's distantly similar to something he can do, but still different. Yet Khan wonders if his own psychic abilities were to make such a meld harder, perhaps more complicated for a Vulcan... and he's unsure if he wants to find out.
What he does know, however, is that Spock isn't offering his services without having to force himself; The displeasure basically radiates off of him in thick waves, so prominent that it's palpable in the air between them. It amuses Khan to a certain degree and the corner of his mouth twitches, but soon relaxes once more.
