TACEVAL Bruggen, seeing off a Jag TBird with an evaluator in the rear seat, for some reason there was only a couple of us in the HAS and I was sitting on the ducting in view and on intercom, but with full NBC kit on during NBC black I had fallen asleep.... The call comes through to go and I'm fast asleep sitting with my respirator on you couldn't tell, pilot is going frantic trying to wave at me and shouting down the intercom without letting the evaluator in the back realise anything is amiss..... Then for some reason I nod and the weight of the helmet wakes me... Afterwards pilot tells me he was considering throwing the contents of the cockpit at me when the rear seater was looking the other way