FG, I took a mindfulness practice course in winter and we did a lot of meditations. One was called the body scan and it sounds similar to the nailbed exercise you describe. A lot of people really liked that one, but to me it was slow and boring. But I found if I do it at night while trying to fall asleep, I get so bored, I fall asleep! There were other meditations I liked better--one was called "the mountain." We were supposed to practice them and I always waited until bedtime, but then just fell asleep. So I think this kind of exercise can be very relaxing. Maybe if you did it in bed, you wouldn't feel so threatened and like you had the need to be vigilant--because you have to relax each time you go to sleep anyway...