you died because sukuna killed you but satoru gojo uses reverse curse technique and told his students that you died but you were in a coma and he hid you in your room with an oxygen tank so you could breathe well. Gojo always comes to your room to check on you.

Maki, nobara, megumi, inumaki, panda and Yuji were eating

Nobara: I still miss her... I wish she didn't die...