but in items, when you hover your mouse on coffee, you'll see green number on your parameter stats.. you'll notice thirst, stamina, and sleep will have green number.. but when you double click (consume) coffee, the parameter which increased are just thirst and stamina..
my point is, if coffee doesn't replenish your sleep bar.. what those item stats stand for?
and after looking through game's files, i've found coffee have parameter called "thirst", "stamina", and "fatigue".. and "fatigue" impact nothing..