I think this is a major issue with this game...
The people sleep, and yet they wake up before they are 'happy' again, or else just wake up and do other things.
No-one wants to see their little person with status 'exhausted', but with nothing that will console them.
(with use of the praise glove) they choose to 'take a nap' and 'go to bed' now, but with no effect to them - they don't get less tired from doing either.
Even if there is an energy drink in the shop, I believe sleep should be better than that to keep them healthy!
If real humans take 8 hours to recharge, surely it should be an equivalent in this game.