To a visitor to the lab, a few days into the protocol the crew of Starship Dinges already look like they've been to the moon and back. The group currently in the lab has been randomly assigned to get a nap of one hour and 20 minutes in the afternoon. Dinges explains sleep inertia as the grogginess and disorientation that you feel when you've been awakened too soon from a deep sleep. There is a large common space where the ersatz astronauts eat, work on batteries of tests and are evaluated physically. The subjects don't completely lose track of time, but lack the time cues that reset their physiology.
Sleep is disturbed radically in space.
It might turn out that sleep can be optimized to promote the secretion of growth hormone, which will keep astronauts healthier longer. They also wear a rectal probe connected to a wrist-mounted sensor unit that measures their core body temperature and arm movements. Dinges insists that the discomfort level is fairly low, which the subjects themselves confirm.