Your body starts to groove to the movement, as in many moving vehicles, from fast cars to slow boats. Psychologically, flying can be a turn-on for a variety of reasons. One reason is the sheer romance of flying. As Freud pointed out, images of flying often symbolize sex in dreams. Think of Superman flying Lois Lane around Metropolis on their first date.
Excitement is also a factor.
Unless you're jet lagged, hung over, or you're just carrying too much baggage, flying is exciting. You're taking off for faraway places. You could meet an attractive stranger, have an adventure. Even if the person next to your isn't so ap pealing, there's always the flight attendant. The hottest ones are a cross between Florence Nightengale, Ameila Earhart and Brittany Spears.