I, too, also wear the pyjamas even on daytime flights, but I suggest that you wait until you are airborne before changing into them. Although it is extremely unlikely, in the event of an emergency on takeoff, you don't want to be running around some field near Heathrow in your PJs and slippers after an emergency evacuation. Call me alarmist if you must, but think safety before comfort. If I have to sprint away from a burning plane, I want to be fully clothed and shod.