That fragile state of being where you haven't gone to bed yet but are on the verge of falling asleep. You know you should get up and go to bed but in doing so there is an inherent danger you will awaken yourself too much by undressing, brushing teeth etc. that you will lose your sleep mojo, rendering you unable to fall asleep.
Steven caught himself nodding off and knew he should go to bed but was afraid he would lose his sleep mojo. So he just let himself fall asleep on the couch. Unfortunately he was late for work the next day since he couldn't hear his alarm going off in the other room.