Dude.

It's natural to be scared of heights. Repeated and frequent exposure to heights will help you to become a lot more comfortable with heights.

But if you take a few months off from climbing, you will need to be re-acclimated to heights.

It's a fear that's hard-wired into out brains.

My wife has vastly improved her fear of heights in the climbing gym. The first time she went, her knees were knocking like two skeletons making love on a wood floor. Now she doesn't have an issue.

What has always worked for me in those types of situations, though I admit I've never really been afraid of heights, is to really concentrate on what you're doing in the moment. Try to concentrate on the area around you as you climb and not think about how high you are. The climbing gym is great for this - when you're in the zone you'll just be climbing and all of a sudden you top out, look down, and think "Damn, I didn't realize I was so high up!".

I spent all of last summer in Yosemite. Before, I used to get vertigo-like symptoms near any ledge. By the end of the summer, I was perfectly comfortable dangling my legs off the Visor on Half Dome (about a 2000 foot drop). The more time you spend around exposed areas, the better it gets.