That problem, whatever it was, did not bother me when I was up, nor did it bother me when I had fallen asleep, but just at the moment of falling asleep -- it felt as if someone had kicked me to the chest, and though I knew from my old experience that it is harmless, it woke me up anyway. All physical sensations** are emphasized at that moment: if someone sticks you with a needle, it feels bad enough, but if he sticks you with a needle just as you are falling asleep, it feels ten times worse.
**and also mental sensations: a nasty thought from the subconscience.
But as I said, it has not bothered me now. Less coffee!