Postorgasmic illness syndrome is a syndrome in which men have chronic physical and cognitive symptoms immediately following ejaculation in the absence of a local genital reaction. POIS symptoms, which are called a "POIS attack",  can include some combination of the following: cognitive dysfunction, aphasia , severe muscle pain throughout the body, severe fatigue , weakness, and flu-like or allergy-like symptoms,  such as sneezing, itchy eyes, and nasal irritation. The symptoms usually begin within 30 minutes of ejaculation ,  and can last for several days, sometimes up to a week. In some men, the onset of POIS is in puberty, while in others, the onset is in their twenties. POIS has been called by a number of other names, including "postejaculatory syndrome",  "postorgasm illness syndrome",  "post ejaculation sickness",  and "post orgasmic sick syndrome".
Postorgasmic illness syndrome
Eight weird things that can happen after you orgasm | Daily Mail Online
As many enterprising people with clitorises know, there are various things you can try to have a better orgasm—and twice as many that will get in the way of it happening at all. Even if you're a pro at the O, experts say you might be hampering your climaxes without realizing it. To determine whether you fall into that camp, mentally transport yourself to those moments when you realize, oh yes, you're about to orgasm , there's absolutely no going back. Now, focus on what your breathing is usually like when you're right on the brink.
This is what happens to your body during an orgasm
The human sexual response cycle is a four-stage model of physiological responses to sexual stimulation ,  which, in order of their occurrence, are the excitement-, plateau-, orgasmic-, and resolution phases. This physiological response model was first formulated by William H. Masters and Virginia E. Johnson , in their book Human Sexual Response. The excitement phase also known as the arousal phase or initial excitement phase is the first stage of the human sexual response cycle, which occurs as a result of physical or mental erotic stimuli , such as kissing , making out , or viewing erotic images , that leads to sexual arousal.
But for some, the big O can bring on some rather unexpected side effects - including hallucinations, crying, sneezing and even an orgasm in your foot. These, and other bizarre symptoms, have actually been reported in scientific literature in what experts call 'peri-orgasmic phenomena'. Psychological responses can also include feelings of love, happiness, and relaxation. Some women have reported feeling the sensation of flying after having an orgasm file.