Don’t cars have two separate, diagonally opposed hydraulic brake systems just so this won’t happen? Why didn’t you still have pressure on the other rear wheel, and one of the front wheels?
I thought so too but that is what happened. I have never experienced anything like it in about half a million miles of driving and it freaked me out. Maybe a mechanic can answer that. Brake pressure went from spongy to almost completely gone in just a few miles. I was able to get it stopped at a gas station and buy 5 bottles of brake fluid just to try to get home and I used most of it by constantly replacing the fluid lost to the leak. As long as I had some brake fluid, I could get a very small amount of brake pressure if I pushed the brake peddle as hard as I could down to the floor but that was about it. I was going to have it towed but I realized that I could take back roads with little traffic and would probably be OK if I stayed in low gear and stayed at less than 15 mph while timing traffic lights correctly. I was lucky that the repair shop is just a block away from my house and they were able to fix it in just a few hours the next morning.
On the subject of “silly things you get tempted to do while driving”, not so long ago I decided to see what would happen if I knocked the manual transmission gear stick into neutral while cruise control was on (without depressing the clutch, which would cancel cruise control). As I suspected, the engine revved wildly, but I got worried and turned off cruise before I could see if it would do it automatically.
And not long after that, I had to replace the dual-mass flywheel (not cheap). I don’t know if these two things are related. 
This varies from one car to another. For a while, I drove an 89 Thunderbird Supercoupe with a manual transmission. I was fairly young and it was the first manual I had driven that even had functional cruise control. I decided to push in the clutch while it was on and see what would happen. Just like your car, it slowly started revving up until I finally let off the clutch pedal or canceled cruise control.
On the other hand, I now drive an 09 RX-8 and did the same experiment. Pushing the clutch canceled the cruise control automatically. It’s very useful for passing people in certain situations. In that car since it has fly-by-wire, I’m pretty sure the ECU handles cruise control and since there’s a clutch pedal sensor attached to it, it easy to program it to cancel unlike my Thunderbird where I believe the ECU had a clutch pedal sensor but not the entirely separate cruise control module. I’m not sure if I’ve ever shifted to neutral in the same way, but since it has a neutral sensor, I’m pretty confident the same thing would happen.
Pressing the clutch cancels the cruise control on my car (a Volvo V50). I was seeing what would happen if I just shifted into neutral without using the clutch, therefore bypassing the cruise cancel. :rolleyes:
(Knocking the shifter into neutral without the clutch is no problem as long as you are just idling, as far as I am aware. In fact it is perfectly possible to drive and change gears without a clutch by rev matching - I once had to drive home that way after the clutch on an old car gave out completely.)
I used to have an RX-8 (loved it!) but didn’t have cruise control on that. I don’t think it was even an option in Europe.
Oh wow, so the clutch canceled it but not shifting to neutral. That’s interesting. I’m going to have to try that now. I have a Mazda Protege as a daily driver and the RX-8 usually stays under the cover. They’re both manuals. I’ll have to experiment with them. (The Protege is ten years older so I wouldn’t be surprised if they give me different results.)
Yeah, it’s easy to slip it into neutral as long as you take the torque off the gears either by giving it just enough throttle or waiting until it’s at idle speed. I do it often coasting to stop lights though lately I’ve been practicing my heel-toe downshifts a lot. It’ll be a little trickier with the cruise control as I can’t control the throttle and I’ll have to find somewhere that’s slightly downhill so the engine is neither pulling or lagging (or just disconnect the clutch switch).