Sex is the kind of thing that can keep you up at night.

In a good way, of course.

But its many attendant mysteries might gnaw at your imagination when you’d really rather be catching 40 winks.

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If knowledge is power, your sex life and gratification only stand to benefit.

The fourth decadeisterrific for sex, but libido probably isn’t why.

The refusal to ask for directions?

An aversion to maps?

Insert your own joke here regarding men’s ignorance about finding the right spot.

Debriefing him on the details is nothing to be ashamed of.

“Men are so grateful when you tell them what you need,” Davidson says.

(Plus, he might wonder what other secrets you’ve been keeping from him all this time.)

Gently explain to him that it’s meant to enhance, not replace, what he’s doing.

That way, you could experience your orgasms within the same century as your honey."

“There is definitely something to the saying ‘Use it or lose it,'” Foley notes.

The same way muscles atrophy from being stagnant, so can the libido.

“But it doesn’t go completely dead.”

Davidson points out that this is because “you’re bringing chemicals and pheromones into the world.”

But the sheer power of mental energy counts for something, too.

If you feel sexylo and beholdit will be so.

When you’re with one person long enough, it makes sense that your creative instincts might kick in.

“Fantasizing can be harmless.

Incorporate your partner into it to build a sexual connection.”

Hard numbers aren’t available, but some research suggests an orgasm can increase the chances.

(Fertilized eggs return to the uterus to settle in for the long haul.)

The ideal time to orgasm is one to two minutes after he’s ejaculated.

“We seek new stimulation for pleasure, but then we habituate to it,” Foley says.

Davidson likens the experience to being a singer who could hit a high note yesterday but can’t today.

“How warmed up are you?

Is your mind wandering?

Is something in the way?”

Jacquie Greaux, author ofBetter Sex Through Yoga(Broadway Books), concurs.

“It means your body is governed by diet and stress, not to mention PMS and bad-hair days.

Be open to new ideas in bed.

Or in the shower.

Or on the kitchen counter.”

What often erodes intimacy is the stress of everyday life: bickering, petty resentments and housework score keeping.

“Relationship issues follow you into the bedroom,” Foley says.

Start by telling your partner you love him and that you should probably get some things off your chest.

Being honest and sharing your feelings will foster closeness in and out of the bedroom.

You don’t merely love to hate her, you live to hate her.

Your own healthy self-protective defense mechanism kicks in, too.

(Let’s face it: You’re not about to fault yourself.)

“You’re over the fatigue,” Foley says.

“And you’re uninhibited because you’re not worried about getting pregnant.”

Either way, take advantage!

“There are shades of gray, especially when it comes to women.”

Testosterone is the hormone of desire, and men have heaps more of it than women do.

“Men’s urges are also more spontaneous and often stimulated by visual triggers,” Davidson says.

“A guy could watch golf on TV, see something that sparks a memory and get aroused.”

Rome was not built in a day.

Neither was the 45-minute pleasurable moan.

to intensify and prolong climax.

“Women seem to be more amorphous in their sexual orientation,” Lippa says.

“Men are much more black-and-white.

The wax appointments start tomorrow!

Photo Credit: T. Kruesselmann/Zefa/Corbis