Sex is complicated and convoluted, yet few people can fight the urge to ward off thoughts, feelings, and desires. But when there are issues in the bedroom, it’s easy for one or both partners to lose their sex appeal. Some experts say a lack of sexual satisfaction could lead to missing a third person in the bedroom (namely, fantasies).
What is a sexual fantasy?

According to Cyndi Darnell, a clinical sexologist, “What makes a fantasy powerful is that it is just that: a fantasy. Its purpose is to help you process things and is not a reflection of any latent erotic desire.” She adds, “We may not actually want to do them. Instead, these fantasies can offer a portal into aspects of our non-sexual emotions that we’re trying to reconcile in our day-to-day lives.”
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What do men and women fantasize about?

More about the fantasies:
BDSM (bondage, dominance/submission, sadomasochism)
Many respondents said the idea of forced sex turned them on.
Novelty, adventure, and variety were also important
It’s not uncommon for people to spice up their sex lives. So what better way to get your adrenaline pumping than having sex in unexpected, surprising, or thrilling places?
Forbidden sex
Sex that‘s a no-no, mainly because it violates what most consider human decency. Still, many in Lehmiller’s survey took pleasure in erotic thoughts that involved illegal acts.
A slight variation between men and women

Lehmiller says women often lust about same-sex experiences and BDSM, while men wanted to engage in acts that involved cross-dressing and taboo behaviors. CNN writer Ian Kerner added, “the top five female fantasies involve having sex with a stranger, being worshipped in bed, being ravaged in bed, being watched by others, and enjoying a threesome. In other words, women tend to fantasize about being the object of desire.”
Side note about men

There’s a widespread belief that men are usually to blame for sexual problems. In other words, men are expected to be leaders in general, including a stellar performance in bed. A man’s ability to perform sexually can be affected by how he perceives his partner’s attraction to him. If he thinks she’s not interested, he may become anxious, which can lead to erectile dysfunction or premature ejaculation.
But some experts say fantasizing during sex, like staring in a porn movie or having sex with someone else, can actually help improve performance.
“Though no one likes their partner imagining someone else while in bed but, sexual attraction in any relationship starts fading after a certain time, and it is okay to fantasize [sic] in order to increase your performance and adventure in bed,” writes TNN. The theory is that men with performance issues can engage in sexual fantasies without getting emotionally attached to the fantasy, so they don’t suffer consequences.
Tell or don’t tell?

Lehmiller found that sex partners focused on one fantasy during love-making. “My results suggest that the one person who is most likely to appear in your sexual fantasies is – believe it or not – your current romantic partner,” Lehmiller said.
He further stated, “I found that most people who acted on their fantasies reported that the experience was at least as good – if not better – than they were expecting and said that it improved their relationship. But it isn’t something you want to leap into or take lightly.”