Bottled Sleep
Potion
Drinking this potion has the same consequences as having a peaceful night of uninterrupted slumber. You drink the potion, wait about a minute or so, and then you will feel as refreshed as if you had just gotten up from a perfect night’s sleep.
You can’t use Bottled Sleep indefinitely, though. If you don’t get some real, non-magical sleep, the potion eventually stops working. With regular sleep, you can get back to the point where the potion is effective again.
Ethan Abides 
So how much “regular sleep” does one need? One night a week and six bottles? One night a month? Every other day?
It’s different for everybody, and can vary even for the same person at different times. Drink the potion. If it doesn’t work, get some sleep. If it still doesn’t work, try sleeping again. Repeat as necessary. Better yet, don’t overuse the potion in the first place. 🙂