He doesn't have a couch???
As for your issue, I wouldn't call it a sin, but it's still not a good thing. Sleeping in the same bed with the opposite sex is temptation, and may lead to stuff.
You said your friend is sick, so he most likely won't be thinking about all that inappropriate stuff, but still it's not a good habit to get into. But yes, like what HelenTn said, it would be smart to bring someone with you to care for him.
Otherwise, if I were you i'd sleep on the floor.