Same problem here, been scared of heights all my life. Just suck it up and go- it gets easier the more you do it, but it still scares me. I talk to myself, things like "Okay, you're halfway across, you can do this!" so make sure your helmet mike is off or your riding partner will give you endless grief.
How the hell I'm comfortable strapped to the side of a helicopter is beyond me.
Read The Patriot Post -- It's Right. It's Free.
Sometimes the light to see your way forward is provided by the bridge burning behind you.