If you don't like heights, maybe your body is trying to tell you something. DIY jobs that require walking on the roof or dangling from a second story window can result in an unscheduled trip to the emergency room. Professional roofers are required to wear protective harnesses for a reason. It's easy to become dizzy and disoriented up in the stratosphere, and successfully swapping out a roof shingle doesn't seem like adequate compensation for the risk.
If you have a roof repair in mind, call a professional. If you absolutely refuse to farm it out, invest in a roofer's fall-protection kit. You can usually find them at home improvement outlets for around $100. They're a harness with mounting gear designed for the DIY enthusiast. If you take a tumble wearing one, you'll only hurt your pride.