At the start of your relationship, there was electricity, passion, and sex--daily, if not hourly! Years later, it's a challenge to remember the last time you were naked together. (Last Thursday--or wait, was it last month?) It's not surprising if you can't recall: Lots of committed couples aren't heating up the sheets as much as they used to, often because women have lost the urge. In one study involving nearly 1,000 women, researchers found that 65 percent of those in a relationship for a year or less reported wanting to have sex often, compared to just 26 percent of women who had been coupled up for three years. Besides taking a toll on your love life, a lack of interest in sex is bad news for your health. "Numerous studies show that people with active sex lives have fewer heart attacks, increased stamina, and a stronger immune system," says Beverly Whipple, Ph.D., a sexuality researcher in Vorhees, New Jersey, and co-author of The Science of Orgasm. Here are six real-life reasons your desire for sex may have waned, and the easy moves to help you get back in touch with your sensual side.