Pon Farr

Pon farr is a neuro-physiological condition in Vulcans from the Star Trek continuum. Every seven years, adult Vulcans experience an overwhelming and irresistible urge to take a mate&mdash;failure to do so can result in death. It is considered an intensely private condition that they rarely speak of with anyone outside of Vulcan society.

If a Vulcan suffering from it mind melds with someone, that someone develops it too, regardless of species. Such was the case between Agents Sebak (a Vulcan) and Five of Six (a Narnian dryad) in 2009.

Pon farr is sometimes used by Sues to justify a relationship with a Vulcan. If done badly (for example, if the Vulcan is open about their condition), it is a charge.

More about pon farr at Memory-Alpha.