For nearly a fifth of men, sex is just terrible.

About 16% of men are able to ejaculate but feel none of the pleasure of orgasm, according to research presented at the European Society for Sexual Medicine.

In fact, when it comes to sexual dysfunction, it's not the erection or the ejaculation that's the problem for many men -- it's feeling anything at all.

So are these men, well, faking their orgasms?

"When I asked the test subjects in plain language, Did you feel orgasm [after ejaculating after sex with a woman], 16 % of men in our group said they didn't have sensation of orgasm," said Dr. Darius Paduch, assistant professor of urology and reproductive medicine at Weill Cornell Medical College.  "This is astonishing."

Problems with sexual pleasure don't just affect older men.  Paduch said that he sees men as young as their 20s.

It isn't easy for men to admit to their partner that they can't enjoy sex.

"Our society is more sympathetic for women facing sexual problems, but men are still faced with self-doubt, fear of being labeled as impotent, inadequate and just not a full man," said Paduch. "You need to remember that regardless if a man is a bricklayer or a president, men value themselves through their sexual performance."