Others have noted an increased sensitivity to internal stimuli when the physical body is about to fall asleep, which

Others have noted an increased sensitivity to internal stimuli when the physical body is about to fall asleep, which may manifest as ‘an awareness that the pores of your skin breathe, hearing the swish of blood flow behind your ears, feeling your heartbeat.’ If this seems difficult to imagine, consider a medical disorder of the inner ear such as superior canal dehiscence syndrome, which leads the sufferer to hear the eyeballs moving in their sockets like ‘sandpaper on wood.’

_Frederick Aardema, Explorations in Consciousness_