You know... I'm a bit confused. Why can't Yui feel her feet?
Also, why does she seem so nonchalant on being 3% HP away from truly dying? Is she just really good at understatements?
Also, ingame, there is still hunger. Players still feel hungry.

The system is set up so that the brainwaves are essentially hijacked by the game and so they feel true sensations from the game. Food has taste, attacks hurt, people get fatigued, people can feel the texture of fine clothes on their body, etc.

People were brought to the hospital within two hours of Kayaba informing the players and the world of the state of things in game.