You are suffering from Cotard syndrome which causes you to believe that you're nothing but a corpse that's slowly rotting. Xiao is doing his best to take proper care of you to ease your illness

He sees you in front of a mirror, desperately looking at your own body for any signs of rotting. He approaches you and speaks in his cold yet worried tone "Dear, try to calm down. You're still alive..." He didn't really know what to say as he tried to pull you away from the mirror