A survey of 2,500 U.S. college students found that a good portion of them experience sadness, regret, and ambivalence the morning after "hooking up."

In her new book entitled The End of Sex: How Hookup Culture is Leaving a Generation Unhappy, Sexually Unfulfilled and Confused About Intimacy, college professor and author Donna Frietas said that our culture pressures men and women to substitute meaningful relationships with temporary flings.

"Students define the sexual aspect of a hookup as 'anything from kissing to sex,'" said Freitas. "To equate a hookup with casual sex is to miss the really important part of the conversation, which is that students feel so much pressure to show they are part of things that they'll count almost anything as a hookup."

Justin Garcia, a sex researcher at the Kinsey Institute in Indiana, told CNN that most college students have had more hookups than first dates. A problem arises, however, when those engaged in hooking up desire more than just sexual gratification from their partner.

"Our data has shown that one of the greatest contributors to hookup behavior is a desire for sexual pleasure," said Garcia.  "However, there are also a large number of college students -- around 50% in one of our studies -- that hook up because they are hoping to start a romantic relationship or want emotional gratification."

According to CNN, of 557 students who responded to a question asking how they feel the morning after a hookup, 41 percent said they felt sad, regretful and confused. Dr. Susan Krauss Whitbourne, a psychologist and contributor to Psychology Today, wrote, "People who engage in casual sex may suffer emotional consequences that persist long past the encounter."

Based on Freitas' research, hooking up is the social norm, but it may not be preferred. She found that many students associate sexuality with boredom, isolation, and ambivalence, and accept casual sexual encounters as part of college life. However, the majority of them said that they do see themselves in long-term, committed relationships in the future.

For now, Freitas encourages young adults to talk about intimacy with their friends and classmates, and to go out on real dates. She also says that college administrators should take on sexual education in a bigger way on college campuses. Handing out free condoms is no longer enough.