The sex may be good, but how's the sleep? The way couples literally sleep together, recent studies have shown, affects not only their health and their happiness as individuals but also their satisfaction with each other.
"The time that couples spend together in close contact after sex is a really important part of a healthy sexual relationship," says Daniel Kruger, an evolutionary psychologist at the University of Michigan.
Most sleep research focuses only on solo sleep. But Wendy Troxel, a psychiatrist at the University of Pittsburgh Sleep Medicine Institute, studies the way people typically sleep in their natural habitat: with someone else beside them.
Although we generally sleep more deeply when alone, "we prefer to sleep with a partner, which suggests a fundamental human need for attachment at night," says Troxel. In his book Two in a Bed, sociologist Paul C. Rosenblatt notes that many couples today spend more time together in bed than on their feet. Making that time harmonious—agreeing on temperature, position, bedtime—requires just as much compromise as the many negotiations of the waking hours: "Sleeping together is an achievement of coordination on many dimensions."
Sleeping next to a snorer or insomniac, however, has its risks, finds William Strawbridge, a sociologist at the University of California, San Francisco. Partners of troubled sleepers have higher rates of depressed mood, relationship dissatisfaction, and "poor" or "fair" physical and mental health. Still, says Troxel, "rather than just choosing to sleep apart, the first step should be motivating your partner to seek treatment."
A study in the European Respiratory Journal reported that when one spouse receives therapy for sleep apnea, both notice a decrease in disagreements. "Be patient with the process, and believe your partner," advises Rosenblatt. "If your bedmate says you snore, don't fight it."
Honey? Are You Awake?
In 1953, pioneering sex researcher Alfred Kinsey discovered that after an orgasm, most people have one of two reactions: They fall asleep immediately or become hyperactive.
Men are more likely to hit the pillow, while women tend to become more energized, says Debra Herbenick, a sexual health educator at the the Kinsey Institute for Research in Sex, Gender, and Reproduction at Indiana University. Physiologically, it's unclear why men often fall asleep first, since bodily responses to sex are similar across gender lines. But dozing off right after sex provides an evolutionary benefit to men: It shuts down the opportunity for a commitment conversation and increases their chances of reproducing with other mates, says Kruger.
Women, meanwhile, are often kept awake by some very unsexy thoughts. "It's common for women to say they continue to go through the to-do list after sex," Herbenick says. "They think, 'I have to go empty the dishwasher and pack the kids' lunches.'"