Checking yourself into rehab for alcohol (Lindsay), drugs (Mary-Kate), or just a case of the crazies (Britney), is so last season. Lately, the buzzword in compulsive behavior is sex. David Duchovny was recently admitted to rehab for sex addiction. The new movie "Choke," by the dude who wrote "Fight Club," is a twisted look at the life of a sex addict. And VMA host Russell Brand has copped to receiving treatment for sex addiction.

In the media and around water coolers, sex addiction doesn't get much respect. It doesn't cause cancer, harm your liver, or lead to embarrassing drunk-dials (though it is dangerous to mix with driving). Everyone likes sex, right, so what's the fuss?

Click here to learn what sex addiction really is -- and how to know what's normal.

What is it? Like with most compulsions, sex addiction is considered a problem when it interferes with a person's ability to function normally. Those who suffer from compulsive sexual behavior are relentlessly preoccupied with their next sex session, whether that's intercourse, masturbation, porn-collecting or some other outlet.

They're often unable to control their sexual desire, even in the most inappropriate of situations. The pursuit of sex can hurt their families, careers and finances (just think of what it did to Eliot Spitzer), not to mention their health and safety. For addicts, sex is often followed by feelings of shame and despair. Sex addictions affect about 3 to 6 percent of American adults.

What causes it? Increased levels of the neurochemical phenylethylamine (PEA) -- the element that makes you feel so blissful when you're in love -- are often found in addicts, which may play a role in their pursuit of physical gratification. As with many mental diseases, an early childhood experience can set the stage for behaviors that become compulsive (Brand's father reportedly took him to a prostitute at a young age).

Is your sex in check? Visit sexhelp.com or click here for a free online screening test to rate your sexuality. For more information read Are My Sex Habits Normal? to see what the experts have to say about your sexual habits.