As Xzin said - /follow used to be a toggle on/off command in wow, but for some reason they changed it a while ago. Now you can start autofollow, but can't stop it through a command. Only way is to start something else. Casting a spell typically doesn't work (flags the error "cannot cast while moving") so, again as Xzin said, i have my "stop autofollow" button as tapping a key bound to backwards.