In the early '70s (probably bored by the first oil price crisis) psychologists Donald Dutton and Arthur Aron conducted a series of experiments.
First, they sent a group of men down a rickety, wobbly bridge across a scary river. On the bridge, a woman asked them to complete a projective test that involves making up narratives about ambiguous pictures. A similar group of men was sent across a safe and sturdy bridge across a small creek and presented with the same test.
Guess what. The men who experienced the scary bridge produced narratives that were much richer in sexual content than the men on the safe bridge. Also, they called the female researcher back much more often (9 out of 18 vs. 2 out of 16 men). The results were corroborated in a later experiment in a laboratory setting with scary shocks, where the men anticipating shocks produced more sexual narratives and reported being more attracted to a female also present than men who didn't experience shocks.
Hm. It looks like our hearts and minds are not very good at distinguishing where flutters and butterflies come from. Scary can mean hot. The nearest potential partner becomes more attractive. Feelings get a boo- st.
What can we do with this? Well, as wobbly bridges are rare these days, I would advocate you ride a roller coaster with your love at least once a month. And take advantage of the current season: check out the neighborhood's scariest displays. No dodging the haunted houses...