Lonely hearts club members get less deep sleep than their coupled counterparts.
We have all seen in the movies, or perhaps in person, a person becomes hypnotized and falls slowly to sleep.
Research shows that marksmen shoot most accurately when their hearts' rhythm increases from eight to twenty beats per minute over their resting heart rate.
There was indeed a connection. Everyone slept for about the same amount of time, but the volunteers who rated themselves as the loneliest were also the ones who were most likely to wake up during the night.