Next time your guy just doesn't seem like he's into getting busy, don't think it's you. It's much more likely because he didn't sleep well the night before.

Researchers from the University of Chicago found that sleep deprivation can dramatically lower testosterone levels, thus decreasing a man's sex drive.

"Low testosterone levels are associated with reduced well-being and vigor, which may also occur as a consequence of sleep loss," Professor Evie Van Cauter, who has been researching the effects of sleep loss for 10 years, told the Telegraph.

Aside from sex, the study also found that a dip in testosterone can lead to a loss of energy, increased fatigue and bad concentration. Researchers have linked the issues to potentially developing heart disease, stroke or type 2 diabetes.

Van Cauter and her team put 10 healthy men with an average age of 24 through a number of tests. The participants spent three nights sleeping in a lab for up to 10 hours, followed by eight nights of less than five hours of sleep. Researchers then took blood samples every 15 to 30 minutes for 24 hours during the last day of the 10-hour sleep period and the last day of the five-hour sleep period. The men also kept a log of how they were feeling throughout the process.

While it's not surprising that the men's moods and health were negatively affected by the end of the study, the blood test also showed a substantial drop in their testosterone levels.

So if you want your man to be good in bed, make sure he's gotten a good night's sleep first.