Suddenly, a Sim would be exhausted, starving, and need to go to the bathroom. They could end up just standing there and crying until they passed out in a puddle of their own pee. All the needs crashed when they came out of the zone.
Now I'm thinking it makes more sense if the needs bars are seen as a Sim's awareness of their own needs. The needs are still changing, but the Sim doesn't know it. Being in the zone is hyperfocus, and it interrupts interoception.