I'm another who's terrified of drops. I eventually plucked up the courage to do ToT, but I'm in no huge rush to do it again; I did Dudley Doo Right's which left me traumatised and I <i>won't</i> be doing it again; I'm still contemplating Jurassic Park; and whilst I do Splash Mountain each trip, the fear is still there! Oh, and Dr Doom - I don't think so!!!
However, Spiderman is a fabulous ride and not scary at all. Like you, I was nervous the first time because I'd read about the 400ft sensory drop, but it's just that - a 'sensory' drop. You don't actually go anywhere. And unlike real drops where closing your eyes just intensifies the sensation, on Spiderman it's always an option. Try to keep them open, though - I promise you you'll love it!