Someone who's confused or incoherent is slaphappy. Going without enough sleep for a couple of days will leave most people slaphappy.
If you're feeling a bit like you've hit your head—dizzy and lightheaded—you're slaphappy. This informal word is perfect for describing the state when you're so exhausted that you start giggling. Slaphappy was first recorded in the 1930s, and it originally described someone who is "punch drunk," or "stupefied from repeated blows to the head," like a slaphappy boxer.