Ok, here's how I work.
1.
If its obvious there's a big problem eg.
BAW123: Engine Fire!
or
BAW123: The wings just fell off!
then you get the works - number one, straight in, all that.
2.
If on the other hand, I'm not sure how urgent the situation is eg.
BAW123: Funny smell in the cockpit
or
BAW123: Ill passenger
then I ask you: ARE YOU DECLARING AN EMERGENCY?
If yes, then you get priority, see 1 above. If no, then you wait, like everyone else.
So, you don't NEED to say PAN but I can't give you priority unless you agree to declare an emergency, or its so obvious that I choose to declare one myself.
Sensible?