Sleep is sleep unless you like him who spends every moment he can sleeping when he has free time. That's not normal and I'm amazed childhood friend is the first person to ask him this question. Remember he's doing everything in his life at the bare minimum to get maximum sleep, I'm guessing its trauma still from his mom dying but no-one got the white coats involved.
This is going against what I said before, but it's manga...and we know that everything goes in mangas
In fact, I personally think this small "drama" isn't the problem....since there's romance in this story, a small amount of such situations is kinda necessary if author's plan is to make love bloom with one of the heroines/FL
IMO, the "ploblem" is the (forgive me for the word play) twisted twist this took.....I mean, author created an unnatural situation where, as I said before, MC now has to choose if he sleeps because he sleeps on kouhai's tighs or because childhood friend "told him to" (Idk how to summarize it better, but I hope ppl get the point) when for 10 chapters, we knew he slept because he just wanted to sleep.
While it's indeed weird that he might sleep for 20hrs/day, IMO it's worse that there's this choice now that twists the flow, since up until now, there was no weight to "is it because kouhai or cf?" on the story