This sadness has a name: post-coital dysphoria (PCD). Ian Kerner, a New York City–based sex therapist, describes PCD as "[feelings of] sadness, anger, and distress generally post-sex and often post-orgasm." You might experience it during a hookup, but it also happens when you're with a partner you feel close to and the sex itself felt pleasurable. In fact, you don't need a partner—PCD can even happen during or after masturbation.
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Not only is post-sex sadness a real thing, it's surprisingly common. A 2015 survey of college women published in Sexual Medicine found that 46% experienced it at least once; 5% reported feeling sad and lonely after sex multiple times in a four-week period. "There appeared to be no relationship between PCD and intimacy in close relationships," the study authors noted. The study focused on women, but it can strike men as well.
In fact, earlier this month, the first study estimating the prevalence of PCD in men was published in the Journal of Sex & Marital Therapy. The Australian research team surveyed more than 1,200 men with an online questionnaire and found that almost as many men–41%–experienced PCD at some point and 20% had in the last four weeks. As many as 4% said they had PCD on a regular basis. “Results indicate that the male experience of the resolution phase may be far more varied, complex, and nuanced than previously thought,” the authors wrote.
Kerner says PCD isn't well researched, but he believes the sadness has to do with hormones. "Especially for women, sex and orgasm can release the hormone oxytocin, which facilitates attachment and connection," he explains. If you're having a casual sexual encounter, you'll still feel that surge in oxytocin. Cue the realization that you're not in a long-term commitment with your hookup partner, and your emotions can be set off. If you are with your SO, your sadness might reflect on unhappiness with your relationship.
Sex also makes us feel vulnerable, and that vulnerability can bring on tears. "Post-sex is a reflective period, and that can bring up emotions and experiences you normally keep under wraps," says Kerner. That in turn may trigger a floodgate of tears and feels. Kerner gives the example of a couple who have fallen into a pattern of fighting and then having makeup sex. "With a pattern of fight, have sex, and repair, the sex may feel great, but afterward, you may realize you aren’t really connected or you're still angry."
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Past trauma can contribute to your post-sex blues too. Survivors of sexual assault, for instance, might feel very emotional if the sexual experience reminded them of being assaulted. In the Australian study, PCD among men was linked to childhood sexual abuse, sexual dysfunction, and psychological distress. People who base their self-worth on how their partner feels about them are more likely to feel depressed after sex—if their partner doesn't treat them with the closeness they were hoping for.
If you experience PCD and you aren't sure why, "it’s a good reason to see a therapist, who could help cultivate some self-insight," suggests Kerner. He also says that giving yourself an orgasm via masturbation, and then seeing where your mind wanders, can help get an idea of what might be making you feel so emotional. Whether you cry, laugh, or have another post-sex reaction, know that whatever emotions you feel are valid.