I am an Airbus Training Captain with another airline, but listening to this would tell me this was a potentially very serious incident and the pilots were indeed right to make great haste back to Heathrow. A loss of consciousness or capability to both pilots is potentially catastrophic - similar to Helios in Athens some years ago. It is a million to one long shot that both pilot should be disabled - quite rightly the Captain would not be hanging about in his efforts to get on the ground. That does not strike me as panic - just pure common sense.