As the saying goes, the biggest sex organ is your brain. No love life, no matter how sweet, is complete without a little imagination. That's where fantasies come into play.

But what do your fantasies "mean?" We asked three sexperts -- Barbara Carrellas, PhD, author of "Urban Tantra: Sacred Sex for the Twenty-First Century"; Melissa Kirsch, author of "The Girl's Guide to Absolutely Everything"; and Lynn Harris, co-creator of the award-winning Web site BreakupGirl.net -- to suss out the psychological origins of the most common sexual fantasies. They also weighed in on which ones are better left just that -- fantasies -- and which you owe it to yourself to try out.

Click through below to see some of the most common fantasies, decoded and demystified.

Your Sex Fantasies, Decoded

    Sleeping With a Coworker
    As a fantasy, sleeping with someone you work with is "a healthy exploration of the forbidden," says Harris, and totally natural. "The tension inherent in the power dynamic sure can be sexy," agrees Kirsch. But as a gotta-go-through-with-it reality? It's the economy, stupid! "Not the best move for job security, especially in these times," warns Carrellas. And even if you manage to have the affair and still hold on to your job? "You've never known awkward," says Kirsch, "until you have to see your ex every morning at the coffee maker." Rent "Disclosure" and leave it at that.

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    Sleeping With a Relative
    If you've just signed a million-dollar deal to pen your memoirs and suddenly realize you've led an unsalacious life, you might consider bedding an in-law. Otherwise: Do. Not. Do. This. While it may be common in women's dreams to have sex with a relative, if you're actively fantasizing about it in your waking life, it might mean trouble. Trouble, as in your subconscious is strongly suggesting you get out of the relationship you're in, or trouble or there may be issues from your childhood that need to be brought out into the open. "The fantasy might be harmless, but it might be too close for comfort -- a possibly unhelpful way of addressing an issue that might be dealt with more straightforwardly, and G-ratedly, in therapy. Check it out with an expert, like a therapist or counselor," says Harris.

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    Sleeping With a Celebrity
    While attempting to act on this one for real might result in an embarrassing photo on the cover of Us Weekly, as a fantasy it's perfectly healthy. "These are the safest fantasies and they're universal, like the guy everyone crushed on in high school," says Kirsch. There may be many reasons why you can't get George Clooney off your brain during sex, it might just be practical: "When you're having sex, it can be hard enough to keep your head in the game with all the other distractions in life -- bills, kids, laundry, or work problems. Fantasizing about a celebrity is a way to focus."

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    Making Out With a Girl
    Thanks to Katy Perry, Jill Sobule, and every man who has drooled over girl-on-girl action, this one often gets a skewed rap. For starters, if you dream of getting down with the ladies, "this does not mean you're a lesbian," says Kirsch, "or that you even want to make out with a girl in your non-fantasy life." The fact that you'd never actually want to go through with this could be what makes it a fantasy in the first place. So Kirsch advises, "Don't be afraid to analyze your fantasies if they're perplexing to you," while Carrellas adds, "Acting it out is great -- if it's a physical turn-on." One more thing to keep in mind, says Harris: "If you're thinking of acting on it -- without telling your male partner -- remember, it's still cheating."

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    Having a Quickie
    A classic panty-twister of a fantasy, for obvious reasons. The UPS-guy dream offers "no strings attached, no travel involved, and a man in uniform -- even if it's one in shorts," says Harris. It's also grade-A healthy, says Kirsch. "Women have these fantasies because it's not something most of us are really able to enact with much success. We fantasize about being able to do it like we imagine guys do, with no emotion involved." For most women, though, that's easier fantasized than done. Besides, says Carrellas, "How would you feel about that delivery guy the next time your J. Crew delivery arrived?"

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    Exhibitionism
    Nobody wants to wind up arrested, and nobody wants her own naughty bits downloaded off the Internet 2 million times. If you're absolutely sure you can avoid those undesirable outcomes then by all means, exhibit away! Extremely hot and very common as a fantasy, exhibitionism (or the urge towards it) is simply your mind's way of enacting the ultimate in sexual self-expression. In real life, it's also "easy to indulge in small, safe ways," says Harris, like "letting him grope you -- or vice versa -- in a restaurant booth, or flashing him when no one's looking."

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    Watching Another Couple
    Many experts believe this is a prelude to having sex with another couple. It could also be that you're curious, since sex is something we normally get to see when we're doing it ourselves (or watching porn). Either way, this desire is "very hot and very act-outable," says Carrellas, who advises looking around for local swingers events. There, you'll find more fun-seeking couples and a safe environment for exploring this fantasy and seeing if you'd like to take further. That anonymity is key, says Kirsch, who suggests "Certain things might be sexy in our fantasy lives, but can prove strangely un-arousing in real life. Seeing your best friend in a compromising position might be one of them."

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    Group Sex
    Three-way? Four-way? Husband swapping? The common thread is that you're really jonesing for physical and emotional sensations you can't get in a usual twosome, according to the book "Your Guide to Sexual Fantasies" by Emily Dubberley: "There are more hands and tongues to satisfy you ... More people to be adored by... And the myriad combinations [of sexual activities] are pretty hot." But whatever your preferred flavor, no need to dive in and order the triple-dip with fudge and nuts right away. First, test the waters to see how far you actually want to take this fantasy. You could start by enacting the just-watching fantasy mentioned above, or try having sex while an adult video plays on the TV. If you're still unsated, discuss with your partner.

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    Videotaping Yourself
    With a new celebrity sex tape turning up daily, is it any wonder that you might fantasize about this? While famous femmes like Paris and Pam have made this sextracurricular activity seem tawdry, it's actually one of the most chaste sexual fantasies you can have; usually this indicates a desire towards things like voyeurism, exhibitionism and group sex, except you're doing all that in the privacy of your own relationship. "The hottest sex toy for many people is a camera," says Carrellas. Since everyone has one (even if it's just the one on your cell phone) it's also very easy to try, with an even easier delete button to hit if you don't like what you see. Just remember that committing your home movies to something more permanent than your flip-phone should only happen when your costar is someone you absolutely trust.

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    Sadomasochism and Bondage
    Not as scary as they sound. If you're looking to build deeper trust in your relationship, then fantasizing about domination and submission is totally normal. And if you're already in a rock-solid relationship, it's a safe way to act out control fantasies (much like the sleeping-with-your-boss fantasy). Either way, "both of these are easy and fun," says Carrellas, "and they can be acted out in a vast variety of scenarios, from tame to intense." A simple slap on the butt during sex is a good start. So is a blindfold, a pair of scarf-bound hands, or the dominant partner simply telling the submissive one what he or she wants.

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