To regain energy and heal wounds, sleep is the best medicine there is.
Well, the best non-magical medicine anyway. You heal fastest if you are
sleeping. Make sure you aren't hungry or thirsty though, you won't heal very
fast if you are.
A word of caution: make sure you are among friends or in a safe environment
before you decide to sleep. Since you are sleeping, you can't keep an eye on
who is around so someone could steal you blind or stick you with something
sharp before you could defend yourself. The damage bonus levied against a
sleeping person is very high so BE CAREFUL WHERE YOU SLEEP!
See Also: Sit, Stand, Wake, Rest