Rack is both a noun and a verb. It is slang for Cocaine.
"Hey man, have you got any rack"
"nah mate, its all gone, i just racked it all up"
Rack attack is the process of taking cocaine, it is also the state which one gets into after too much cocaine.
Mike : Yo dude, want to go for an attack?
James : Of course!. Lets go
5 minutes later...
James : Man, i'm having a rack attack.
Mike : Me too, i've been severely attacked.
James : Lets go for some more