Almost 20 years ago back in college I borrowed my then girlfriend's parents' Datsun Z, which was not in the best of shape, for a drive from California's central coast to San Francisco, Oakland, and back (500 mile round trip). I had had very little experience with a manual transmission, I did most of the freeway drive in 3rd because I thought it was fifth (and I was afraid of accidentally putting it in reverse so I avoided 4th altogether), and couldn't figure out why this "sports car" couldn't do more than 70 mph. I made a habit of feeling around with my left foot for the clutch pedal once in a while to make sure I knew where it would be if I needed it (dummy check), and I did that once and it wasn't there. My left foot was moving from the brake pedal to the door and I somehow could not locate the clutch. I even tried to look down with a flashlight while driving 70 on the freeway and couldn't find the thing, tried reaching down with my hand while keeping my head barely above the dash to see. Thought I was going crazy. I finally got disturbed enough to pull off the freeway, had to stall it to get it to stop, then put on the parking brake and got down on my knees with a flashlight to find the clutch pedal had sunk down to be level with the floor. I had no idea this was possible, or how it could happen, or what I should do about it, or if it would keep happening. I pulled it up to its proper position and it stayed. Pushing on it disengaged the clutch just like it should. I didn't know what else to do so I continued the drive, but the entire time I kept my left boot wedged firmly under that clutch pedal to make sure it wouldn't sink on me again. Didn't have any other problems with it, though.