That is normal for them to sleep standing even if you tell them to sleep on the floor, that is by design of the game
I know they are able to sleep standing, but they usually only continue standing if there wasn't enough space for them to lie on the floor and if they are standing, when you move them to a place there is enough flat space for them to lie, they will fall over. However, that now never happens. Even when they pass out on their own, they never fall on the floor no matter where I place them. There's probably some conflict between mods somewhere . . .
So for now, I'm just going to go back to use aliasthepal's similar hack. I think yours stopped working correctly around Pets (I know it's been a while, and I never investigated it fully), and someone else over at MTS2 mentioned that they had the same problem as I do with Sims always standing when they fall asleep with your hack, so he/she probably has a similar conflict. But no probs, though. Still love all the work you do and sorry for not stating clearly what the issue was in the previous post (and also taking forever to reply) :^D