What actually happened with the parking brake?

A few weeks ago I accidentally left the parking brake on for a 25 mile
drive, highway in the middle with about five miles on each end that were
side roads.

On the last five to seven miles, the brakes went to the floor when I first
pressed them, and that's the first time I knew there was a problem.

I figured out only then that the parking brake was on, which I released,
but the brake pedal still went to the floor like there was nothing there.

I did have braking though, if I pumped the pedal on the early 2000s
econobox FWD car, and I let it sit outside to cool off overnight.

In the morning the brakes were fine and they've been fine since then.

I'm just wondering what actually happened to make the brake pedal go to the
floor, and then, when it cooled off, it fixed itself?