Spice - this is reasonably well documented in the military - suddenly after years of operational flying, the realisation that flying can be risky finally breaks through from the subconcious where it has been suppressed to the conscious where it manifests itself as fear of flying. I think it's a bit like stage fright in that if you don't think too hard about what you are doing, the scary reality can be ignored. Rationalising your fears is the way to cope - put the perceived risks of flying into perspective by comparing the much more real risks of driving to the airfield or crossing the road.