ways to keep your sex life alive

Sex is priority number one – who cares about sleep? Or work? Or really anything that doesn't involve getting naked? But over time, the urgency to tear off each other's clothes gives way to more mundane activities, such as eating breakfast and showering. Nobody plans for the heat to dissipate. It just does.

The first signs of a sex slump often appear around the two-year mark, when you've settled into a comfortable long-term romance. "As your relationship gets better and more secure, the sexual excitement may fade," cautions couple’s and sex therapist Dr Jane Greer, author of What About Me?

The hormones that are responsible for boosting your bedroom bliss pull a disappearing act right when you need them most.

Scientists aren't exactly sure why things fizzle, but they suspect it has something to do with evolution.

"In the human species, newborns have the best chance of survival when they have two parents during their first couple of years of life," says biological anthropologist Helen Fisher, author of Why Him? Why Her? "So whether or not you decide to have kids, you're hardwired to form a strong two-year sexual bond, which acts as superglue to ensure neither parent leaves for another mate while the child is still developing."

That's not to say you can't tinker with that wiring. In fact, simply switching up the types of sex you have can completely reinvigorate your relationship in ways you've never imagined.

Behold the four kinds of sex that experts say you should add to your repertoire...