How many of us have used the line “Not tonight, dear, I have a headache”? So many that it’s become a national cliché, the stuff of sitcom parody. Yet for a fair number of people with HIV, one night’s lack of desire can spiral into full-fledged sexual dysfunction.

The reasons for this are as varied as they are complex, involving the emotional, psychological and physical. It’s hard to feel sexy when you know you’re sick or are actually feeling the physical effects; even harder when your body conspires against desire by knocking your hormonal or emotional balance out of whack.

When I first became seriously ill with chronic-fatigue syndrome four years ago, sex was the last thing on my mind. I spent most of the day in bed -- and I wasn’t having fun. Compounding the problem: As my desire for sex dwindled, my yearning for the many satisfactions attendant upon a vital sex life grew.

In my case, interest waned as my physical symptoms expanded. But for the largely asymptomatic HIV population, there may appear to be nothing physical standing in the way of a vibrant sexuality. Finding a partner post-diagnosis is less problematic than it was. Serodiscordant relationships as long as a lifetime or as short as a night have become commonplace.

So what puts so many people with HIV out of the sexual loop? “Most of us don’t realize that our hormones are fluctuating,” says Joshua Rosen, a 30-year-old accountant who has been HIV positive for a decade. Unlike many, Rosen never lost his desire for sex, but his ability to have and maintain an erection or achieve orgasm was severely compromised. “I didn’t know what was wrong,” Rosen says. “The majority of people with HIV have low testosterone, but most doctors don’t test for it. They don’t see sexual function as a very important issue.”

Checking hormonal balance isn’t a standard part of HIV spectrum lab tests; you have to ask your doctor. And the results may be as confusing as the initial lack of desire. “A clear range for testosterone levels hasn’t been established,” says Dr. Judith Rabkin, a professor of clinical psychology at New York State Psychiatric Institute in Manhattan. “The range is broad, 300 to 900. So a 25-year-old testing at 370 is technically in the normal range, but he may be feeling totally sexually dysfunctional.”

In groundbreaking studies funded by the National Institutes of Health, Rabkin has been charting since 1989 the effects of testosterone therapy on men with HIV, with such success that only 10 percent of her patients do not improve. Rabkin uses weekly or biweekly testosterone injections in her clinical trials. Testosterone patches are also available. In addition to restoring horniness, testosterone can elevate mood and prevent muscle wasting, with few serious side effects.

Los Angeles college instructor Maria Aversa, 34, has been positive for four years -- and fighting sexual dysfunction. But as Rabkin explains, profound complications like masculinization preclude the use of testosterone in women; however, studies are under way to investigate the effects in women (and men) of DHEA, a “precursor” hormone that the body converts into testosterone. Aversa found that some of her medications contributed to her diminished sexual drive. “The drugs I was taking for depression, insomnia and skin problems all knocked out my sexual interest,” she says. “Changing medications made a big improvement.”

Hormonal therapy or even altering drug regimens doesn’t always work. But many other therapies deal with approach to sex.

Don’t goal-orient sex. Viewing sexual function the way you would a game of racquetball may put orgasm even further outside your reach, and the pressure to achieve it may create new problems with maintaining an erection.

Focus on the sensual and affectionate. So maybe your sex life was once Wagnerian grand opera, and now it’s more of a Brahms lullaby: Appreciate it for what it is. Atlanta psychologist Dr. Virginia Erhardt notes, “It is not true that sex has to be either exciting but meaningless or loving, boring and mundane. Allow all of yourself, not just your genitals, to reverberate with sexual vitality.”

Intimacy is what most people need above all else. For those with HIV, this longing is often magnified. How we achieve intimacy may be through sex, or not. Don’t give up touching, holding, petting, stroking and caressing because you can’t always have erections or orgasms. Don’t give up on sexual expression because it isn’t the sort you’re used to. All of us, sick or well, need to touch and be touched by others. And all of us, positive or negative, can find ways to create exciting and fulfilling sexual lives. Let your mind ignite and your body will catch fire.