There is a surreal trickiness to traversing that in-between area, when the grip of consciousness is slipping but has not quite let go and curious mutated thoughts pass as normal cogitation unless snapped into clear light by a creaking door, or one's bed partner shifting position on the remarkably noisy sheets. The little fumbling larvae of nonsense that precede dreams' uninhibited butterflies are disastrously exposed to a light they cannot survive, and one must begin again, relaxing the mind into unraveling. Consciousness of the process balks it; the brain, watching itself, will not close its thousand eyes. The brain, circling in the cell of wakefulness, panics at the poverty of its domain -- these worn-out obsessions, these threadbare word games, these pointless grievances, these picayune plans for tomorrow which yet loom, hours from execution, as unbearably momentous. Life itself, that agitation of electrified molecules, becomes a captivity, a hellish endless churning, in which one is as alone as Satan, twisting and turning and boring a conical hole in the darkness, while on every side the wide world gently, blessedly snores.
This is a lively, lifelike evocation of the experience of falling asleep, what I sometimes call "negotiating." Sleep often is standoffish and has to be courted. Somehow. The contradiction is much as Updike describes it -- the mind can't talk itself into sleeping, the more attention paid to the goal the more frustration at its receding from the grasp.
Updike (at least in the excerpt) does not explicitly express envy at the triumph of the sleeper nearby. I think it's implied, though. Early in the passage Updike blames "a creaking door" and "noisy sheets" for interrupting the descent toward sleep. Again there is the self-restraint; he holds back blaming that innocent snore for his own failure to fall.
Because translation to sleep is so tricky for me I almost always have to do it alone. Once my body's had some practice I can switch over to the other bed, the bed where the beloved breathes under sleep's gentle guidance. We both, then, may enjoy the unconscious under the single sheet.
I found the passage in a collection of excerpts published in The New Yorker of February 9 & 16, 2009 celebrating Updike's many contributions to the magazine.