1) to get absolutely off your head, usually on alcohol and drugs but can be used to mean just get pissed.
2) to be confused.
P1: this weekend is gonna be deadly!!
P2: i know i havent been madded in ages.
david blaine: and now i will eat my own head twaa...
*eats his head*
P1: wow!! how the fuck did he do that????
P2: i dont know, that has just totally madded my head