Wife and I rode our Trek 2000 along this route http://connect.garmin.com/dashboard?cid=4770928
which includes a bit of a climb (4+ miles) for us flatlanders. We planned to stop at a pub at Fulking after a high speed descent, but when we got to the pub, I slowed for traffic, but didn't stop. When my stoker asked where I was going, I said I didn't know and that everything had gone blank. At first she thought I was kidding. She got me to sit down in the parking lot and asked a number of questions, none of which I remember, but I could tell her our UK and FL addresses. I could not remember anything from that morning, like going to the store for bread, riding up the hill or why we were where we were. After about 20 minutes, I was more or less OK and have been since, but it was pretty scary for my wife. I didn't go to a doctor, but did a Google self diagnosis and determined it to have been transient global amnesia.
It is rare and occurs mainly in men over 50 and usually after sexual intercourse or extreme exertion!! Beware!