If the fear is of something unpredictable/unexpected happening to cause a crash i.e. a front tire blowing, then yes, I would agree that there is a 'mental' block...
Most of what people deal with is more of a vision and process issue. If you aren't looking far enough down the road then everything will seem to be happening very fast, and you become overwhelmed and feel that you cannot react quickly enough. In trying to enable yourself to react to the things that are coming up faster than you can process you will tighten up and get stiff, it's just human nature, but that makes the sensation of speed increase and your fear as well.
My experience with motorsports has taught me that if I have proper and sufficient reference points, and am looking far enough down the road, there is very little sensation of speed. I'm just moving from point to point on the track and adjusting my speed to accommodate the various 'features' of the track. When I have done my best laps, they have felt 'slow'...
To take this to the road on a bicycle, you can't always know every corner on a decent so you have to keep a more conservative pace, but the process is still very similar to me, very much like the first time on a new track. I'm looking for reference points, where to start and stop braking, where to initiate my tip in, where to apex, where I want to be on exit etc. None of this is causing any stress, I'm just working thru the problem. I don't allow myself to carry so much speed as to cause any 'panic', that's counterproductive because it gets you thinking about what you don't want at the expense of what you need to be thinking to get what you do want. The only time I consciously think about speeding up is when I've miscalculated and have obviously not carried enough speed, then I try to work out what I should have done and make a mental note for next time, if there is a next time and if the re-calculation doesn't distract me from acquiring my next reference point.
Some of this is the same in the drafting situation, if your starring at the 'draftee's' rear tire, you have to save room so that you can process and react. If you're looking up the road and seeing what he's seeing, you can anticipate and keep the 'panic' at bay.
None of this is natural, or easy, it takes practice...
I've found that Keith Code has some pretty good explanations...
[ame="http://www.amazon.com/Twist-Wrist-Motorcycle-Roadracers-Handbook/dp/0965045013/ref=sr_1_3?s=books&ie=UTF8&qid=1280572359&sr=1-3"]Amazon.com: Twist of the Wrist: The Motorcycle Roadracers Handbook (Vol 1) (9780965045018):…[/ame]
HTH,
Dave