Hawkphoto - a few weeks ago I was chatting to a colleague at work who told me about a ride he was doing some months back. He'd been out for a few hours, and he came to a steep climb and as he rode over the crest, he got his breath back for the downhill. He said everyting was going just fine, he was picking up speed, got his riding line nicely planned, and he was 'getting' into it. For some reason, though fully conscious, he 'lost' his awareness of what was going on around him, and he slammed into a tree in excess of 25mph! His bike was utterly wrecked. It knocked the wind out of his sails, as you can imagine, and though he felt little pain, he made his way to the local hospital where they removed a sharp piece of the tree that had passed through his arm. He showed me the scar, it is ragged, and he had to have surgery to remove it. He said he still does not know how it happened.
I think it was in the same category as a runner I read about, who supposedly got so wrapped up in the run, that he apparently ran over a cliff, and was killed. Could be an urban legend, I don't know?