When one suddenly cannot breath, feel one's legs, loses the ability to talk, or all of the above due to the thought or sight of Robert Pattinson (aka Edward Cullen from Twilight).
Pattz is an abreviation of Robert's last name: Pattinson.
Gracie: "OMG did you see Twilight the movie?!?!?!"
Janet: "Of course! I saw it 3 times on Friday!"
Grace: "Robert Pattinson is so hot that i had a Pattz attack in the theater."
Janet: "OMFGZ ME TOO!"