[@Paradoxial] I suppose the way you could word it is that he doesn't [b][i]feel[/i][/b] the effects of hunger or drowsiness meaning while he can push himself harder for longer, he will sometimes literally just pass out from hunger and sleep deprivation because human biology can only go so far. He won't feel or think he's hungry, but he is sure as hell going to feel the effects and they will definitely be visible on him.

Also, he will likely be suffering from hallucinations in addition to the voices because your brain does trippy things when it doesn't sleep. I know someone who did an expriment to see what does a lack of sleep do on your cognitive abilities so he didn't go to sleep for like three days and did simple math problems every night. The thing only lasted three days because by day three he was seeing things that weren't there and were scaring the shit out of him like a giant spider the size of a wall mural that kept following him around his house and that batman was on his doorstep and proceeded to knock him the fuck out. This may all sound funny, but you gotta remember that the Wal will get people to think of some scary shit. Plus seeing people where there are non is terrible thing when your party is already on edge or in a fight.