“The more one is occupied with the solution of dreams, the more willing one must become to acknowledge that the majority of the dreams of adults treat of sexual material and give expression to erotic wishes," wrote Sigmund Freud in the first line of his famous Sex in Dreams. In other words, dreams and sex are inextricably intertwined. 
 
 According to data collected by the Kinsey Institute, 37 percent of women aged 45 have experienced an orgasm caused by a sex dream; five percent reached orgasm for the first time after having a dream. As for men, 83 percent have experienced a nocturnal emission; whether or not it was prompted by a dream was not specified. Erotic dreams are abundant in the REM worlds of both genders, with 70 percent of women and 100 percent of men having overtly sexual dreams. 
 
 But is there a way to induce an x-rated experience? Not exactly. But you can increase your chances. The journal Dreaming published a study that found those who slept on their stomachs with their arms raised above their heads were more likely to have x-rated nighttime episodes. 
 
 For the study, 670 students were asked to self-report their dreams and sleeping position. Those who frequently slept on their stomachs were more likely to experience dreams relating to “sex,” “being tied up,” “being unable to move” and “being locked up.” The most common theme was “erotomania,” also known as De Clérambault's Syndrome — the belief you have a wealthy, often famous, secret admirer. 
 
 What makes those who lay prone so, well, prone, to such dreams? Researchers believe that the position puts pressure on the genitals and that external stimulus gets remixed into our internal movies. 
 
 "I believe that the brain during sleep is not at all totally detached from the external world, and stimuli, including those stemming from the environment, are probably incorporated into dream content more often than people observe or are aware of," said lead researcher Kai-Ching Yu when the study was first released. "The unconscious brains of the dreamers try to make sense, and even make use of, the external stimuli." 
 
 If you want to increase the chances of nocturnal trysts, however, know that sleeping on your stomach is actually one of the worst ways to conk out, as it compresses the spine leads to lower back pain. Worth it? You decide. 
– Matt Berical noticed that his restless nights always ended with him facing right, while his girlfriend mostly reported nightmares after waking on her left. "Is there, I wondered, a correlation between bad dreams and sleeping position?" writes Berical at Van Winkles. He dug up a 2004 study that asked 45 men and 18 women to sleep on one side or the other and fill out a popular sleep questionnaire called the Pittsburgh Sleep Quality Index (which evaluates sleep using seven factors, including "subjective sleep quality," sleep duration, and use of sleep drugs). The study found that just 14.6% of right-side sleepers reported bad dreams, compared to 40.9% of their lefty counterparts. Right-side sleepers also reported more dreams with feelings of safety or relief, but had worse-quality sleep than left-siders. Berical also found a 2012 study that analyzed the sleep positions and dreams of over 670 students. The study found that face-down sleepers had more positive and vivid dreams, which were more often about "sex," "being unable to move," "being tied up," or "being locked up," Van Winkles reports. The researcher behind that study, Calvin Kai-Ching Yu, concluded that "the brain during sleep is not at all totally detached from the external world," adding that "the unconscious brains of the dreamers try to make sense, and even make use of, the external stimuli." Berical's conclusion? "It can’t hurt to roll your loved one over when you sense a nightmare coming on," he writes. "Assuming you can avoid the flailing arms, that is." (It turns out that humans are incredibly good at sleeping.)