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There are quite a few words you’d associate with orgasm: pleasure. Release. Satisfaction.

But there are some that probably wouldn’t cross your mind — hallucinations, sneezing, and severe fatigue, for instance.

They might sound crazy, but those symptoms have actually been reported in scientific literature as unusual side effects of the normal orgasmic response — which experts refer to as something called the “peri-orgasmic phenomena,” according to a new review in Sexual Medicine Reviews.

A typical orgasm — which the scientists define as the peak physical reaction to sexual stimulation — can include whole-body and pelvic sensations, as well as flushing, increased heart rate and blood pressure, and heavy breathing, the researchers say. Psychological effects can include feelings of happiness, love and relaxation.

But with peri-orgasm phenomena, some physiological or psychological effects occur that fall beyond those normal responses. Here, the 8 strangest side effects that can be triggered by an orgasm.

Orgasm side effect: Hallucinations
In some cases, your skills in the sack can take her to another world. Of nearly 50 women who claimed to experience “expanded sexual response,” 76 percent to 100 percent noted a flying experience or sensation of flight, according to a 2011 study from Turkey.

What’s more, up to 24 percent noted a sense of entering a cartoon world, up to 75 percent noted a feeling of leaving their bodies, and up to 24 percent listed déjà vu as a component, too.

Orgasm side effect: Sickness
It’s called post-orgasm illness syndrome, and it’s a constellation of symptoms that have been reported in men after ejaculation, including severe fatigue, intense warmth, and a temporary flu-like state.

Basically, your body mislabels proteins in your own semen as foreign invaders, which ramps up your immune response and makes you feel sick. Post-orgasm illness syndrome can be difficult to diagnose, but if you think sex is linked to your symptoms, make an appointment with an allergist, said Mohit Khera, MD, MPH, a urology professor at Baylor College of Medicine. That can help ID a semen allergy.

Related: 3 ways sex can make you sick

Orgasm side effect: Weakness
Orgasmolepsy — the sudden onset of weakness that occurs with orgasm — was first reported back in 1928, and usually occurs in connection with narcolepsy or other sleep disorders. Symptoms typically last for less than 30 seconds and include a complete loss of muscle control.

Prevalence rates of orgasmolepsy differ among studies, but one of the highest-powered listed it as 22 percent among those with sleep disorders.

Researchers aren’t sure what causes it, but they believe firing of the amygdala response — coupled with hypocretin deficiency, which occurs with narcolepsy — may be to blame.

Orgasm side effect: Crying
Crying after sex is a symptom of something called postcoital dysphoria, a constellation of after-sex effects that include tearfulness, melancholy feelings, depression, anxiety, or agitation. They can appear up to an hour after sex, and often occur in stable relationships, researchers say.

Nearly one in three female University students reported experiencing at least one symptom of postcoital dysphoria at least once, a 2011 study in the International Journal of Sexual Health.

It can be alarming to see your partner cry after sex, but it might just be a biological reflex to the hormonal and neurological that occur with it, Lori Brotto, PhD. Or, she may feel lonely after the intimacy of sex is over.

Best way to find out? Give her a chance to talk about it — here’s how.

Orgasm side effect: Sneezing
Case reports linking sneezing to sex have been around since the 1900s — in fact, one from 1972 detailed a 59-year-old man who developed severe sneezing and a runny nose after orgasm, which continued for 10 years.

Researchers believe that activating one part of the parasympathetic nervous system during orgasm may actually trigger a different branch of it, too, which sparks your sneezing symptoms.

Orgasm side effect: Pain
Pain with orgasm can occur in women even if she doesn’t feel pain with intercourse. In fact, a 2009 study described three cases of women who experienced it, even without any anatomical or infectious causes of pain.

Guys aren’t immune, either — men with chronic prostate disease have also been known to experience pain with orgasm, too.

Orgasm side effect: Foot sensations
According to a 2013 case report in the Journal of Sexual Medicine, a 55-year-old woman complained of “undesired orgasmic sensations” that originated in her left foot — which was the same feeling as when she was having sex with her husband.

In fact, whenever she experienced a vaginal or clitoral orgasm, she felt the same sensation in her left foot afterward. The researchers believe it may be due to partial regeneration of damaged nerve fibers in her foot.

Orgasm side effect: Headache
Headaches caused by orgasm belong to the type 2 category of headache: Those which are bilateral, explosive, and triggered by some kind of excitement.

The duration of orgasm headaches can range from several minutes to three hours, and may be alleviated with antimigraine meds or pretreatment with propranolol.

Additional reporting by Ali Eaves and Cindy Kuzma

First published on MensHealth.com