Consensual sex is supposed to be a fun thing that makes you feel hot and great, right? That might lead you to believe it could only ever leave you happy, and never sad.

But thanks to a brand new area of research into the variety of responses humans have after sex, researchers know this isn’t necessarily true for what could be half of the general, sex-having population.

Post-sex blues, or Postcoital dysphoria, is an incredibly common but incredibly under-researched phenomenon that makes people (yes, both men and women) feel sad, angry, depressed, and anxious after an activity that’s supposed to leave them feeling like they’re on top of the world. We don’t know much about it yet, but what we do know should leave you feeling reassured if this is something you experience in your own sex life.

BIG GIRLS (AND BOYS) DO CRY

They also sometimes feel bad after a seemingly great thing. A small but groundbreaking study (one of the first of its kind) from October 2015 found that 46 percent of the 230 female college students who participated experienced postcoital dysphoria at least once in their lifetimes. That means that just about half of all sexually active young women can probably recall feeling melancholic, anxious, angry, depressed, or aggressive after sex, even if the sex itself was great, and even if the sex was just masturbation.

Robert Schweitzer, Ph.D., a lead researcher of the study, told Cosmopolitan.com that about one percent of the respondents (which were all women) said they felt blue after sex every single time, and based on the feedback he and his research team have gotten since the study was published, he believes postcoital dysphoria might also be common in men. But again, since his study is one of the first ones out there about post-sex sadness, it’s hard to know how common this feeling is, exactly. “We don’t know terribly much because it’s so counterintuitive to the dominant thinking about what sex should be like,” he said. “But it is more common than anyone expects.”

Schweitzer said people have described the feeling as “an experience of anger or shame,” and “a loss of self.” One 20-year-old man quoted in a story about postcoital dysphoria in the New York Times described his experience as feeling “literally achy and depressed for about a day.” But a really common description that comes up is “homesickness,” or like you feel out of place in your own body. These feelings aren’t always accompanied by tears, and sometimes there are tears without the feelings. Both phenomenon are equally confusing, but neither should make you feel isolated.

CRYING ISN’T CAUSE FOR A BREAK-UP

What Schweitzer’s study found, aside from the fact that we have far too little research into a phenomenon that could affect many people, was that you might have the best orgasm of your life with a person you love very much and still feel mysteriously blue afterwards. Or in his words, “there appears to be no relationship between [postcoital dysphoria] and intimacy in close relationships.” His study actually focused only on consensual sex between happy partners. So postcoital dysphoria isn’t a sign you should end things with your partner.

Megan Fleming, Ph.D., a clinical psychologist and sex therapist based in New York City, told Cosmopolitan.com that if you find you only experience postcoital dysphoria with one specific partner, you might consider what about that partner or the particular situation is making you feel sad. “If it’s all the time but not with all partners, I’d be more curious about what is it about this particular partner,” she said.

But if after-sex sadness is something that happens intermittently, with various partners, throughout your lifetime, it might be unfair to blame your partner for those feelings. As Schweitzer said, “there’s a lot of rubbish being written that the person [with postcoital dyshporia] hasn’t met an appropriate lover, and that really is just nonsense.”

ORGASMS ARE A SERIOUS RELEASE

While an orgasm can physically feel like the building up and (incredibly gratifying) release of pressure, they can also trigger emotional releases, as well. Fleming refers to this as a pressure cooker situation, and says sometimes an orgasm might trigger a release of things you’ve been writing off throughout the day, week, or month and that could be causing you to feel sad or somehow off.

“Sex can certainly be an experience of letting go and losing oneself, it might be that it’s the point of orgasm,” Fleming said. “It’s like all that stuff that’s been bubbling up under the surface is released. Everything you’ve been holding back, there’s this huge exhale.”

You might not realize it, but as Fleming said, all those things you think you’re letting go of are actually just being emotionally stockpiled, and when you experience something as powerful as the release of an orgasm, you might also release a bunch of feelings you meant to kept hidden or thought you’d discarded. It’s totally normal, but still can be disarming and unexpected.

IT COULD BE SEXPECTATIONS VS. REALITY THING, OR NOT

Quoting a woman who answered his survey, Schweitzer said he believes that for a lot of people, the crash they feel after sex happens because they don’t fully understand what a sexual experience is supposed to be like. “I’m reading a quote in front of me, ‘Maybe it’s to do with sexual expectations, like sex is meant to be one thing — beautiful and loving — and maybe for me, it’s not,'” Schweitzer said. “‘After counseling, I wondered if the blues in me could be fixed. It’s confusing, I feel stuck when it happens.'”

Because psychologists and researchers don’t know much about what goes on in the brain during sex (much less afterward) that could cause such a decline in mood, they don’t know what causes postcoital dysphoria, exactly. The 2009 story from the Times, written by a psychiatrist who’s seen patients with postcoital dysphoria, described using a certain type of antidepressants called S.S.R.I.s (Prozac is an example) to treat the “after-sex sads.”

As he explained, he prescribed these drugs to a few patients in order to “exploit the usually undesirable side effects of the S.S.R.I.’s for possible therapeutic effect.” Those side effects include things like a lower sex drive. In his limited trial, he found that while people generally enjoyed sex less intensely while taking the drugs, their mood after sex was more stable.

But that method isn’t widely used by any means. Schweitzer said that there’s no proof yet that there’s any tie between other mood or mental health problems like anxiety or general depression and postcoital dysphoria. His research team also looked to see if there might be a correlation between a history of sexual abuse and after sex sadness and didn’t find one that’s significant. This basically means that you can have a very happy, healthy, and loving sex life and still feel inexplicably sad when you orgasm.

It doesn’t mean you’re broken, it doesn’t mean you don’t love every minute of the actual sex, and it doesn’t mean your sex life is somehow fucked up. It just means you — and probably half of everyone you know — are affected by a very common but (for now) very mysterious phenomenon that goes against everything we’ve been led to believe about the beautiful experience that is sex. Schweitzer said he can’t exactly give advice to patients who he hasn’t seen, but he wants people to know “they aren’t the only ones.”