The more you race, the more your body figures out what you are about to put it through, and starts to make excuses and tell you lies....
Stand on nay start line and listen to the number of runners who weren't going to run that day due to an injury, and watch them go set a PB....
The paranoia is totally normal and will only get worse the nearer you get to your ace, and the more you race!
To be honest, I cant ever recall heading to a race thinking "I'm in perfect shape for this with not a niggle or a twinge to concern me...."
Its also amazing how those creaky knees and sore toes suddenly vanish if you get a PB!