One of the greatest things about riding a bike or racing one is bombing down a hill as fast as you can, right? If you find descents over 30 MPH terrifying you aren’t alone, lots of riders do. However if you can learn a few tricks it’s not so bad and you might even crack a smile.
As you approach a downhill section of your ride make sure your hands are in the drops. This will lower your center of gravity. Keep your elbows bent as this will help you to relax and help you make finer steering adjustments.
If you still feel unstable try pulling your knees in to grasp the top tube of your frame. When doing this your body contact to the frame acts as extra road dampening.
If you find your self wanting to go faster in your descents make sure that your feet are parallel to each other instead of one pedal up and one down when coasting.
If none of the above makes you feel better or faster or you have developed a speed wobble take your bike to your local bike shop and tell them what is going on. You may need some work done to your bike or even a bike fitting done.