My biggest phobia is the sensation of falling.
I'm not afraid of heights per se - I'm fine with flying, I love overlooks and the top floor of skyscrapers and the kind of views you can only get from on high. That said, I am an utter and complete chicken-shit when that view/height/whatever isn't protected and enclosed somehow by a fence or guard rail or, ideally, a wall with a window.
Examples:
Referenced here, going in the lighting rigs of the Chicago Lyric Opera.
Putting a brave face on it at the Cliffs of Moher. I say no thank you to the idea of plunging 700 feet from a muddy path into an ocean of certain death, thanks.
Also, Grand Canyon. David's ability to just sit and hang over the edge? Not for me, not at all.
This was the closest I got to the edge...and you can honestly see the terror in my rictus grin and clenchy fingers.
The worst for me is when I have the kind of dream, or in-between sleeping and wakefulness moment, when I actually feel the sensation of falling without ever moving. The sick swoop of my stomach, the moment of impact seconds away, and jerking awake with a flood of adrenaline to every nerve...I inevitably never really get back to sleep after that.
I can handle spiders, can deal with the dark, but falling in general...not so much. Make of that what you will...maybe I'm a control freak? Maybe I can't let myself just go? Who knows...per Freud, these dreams can symbolize anything from "a traumatic experience in childhood" to "a fear of the loss of self-control" or "a decline of the accepted moral standard."
At any rate, don't ask me to go skydiving, and if you're headed to Splash Mountain, I'll happily take pictures from the sidelines.