After about 30 minutes of extreme stop and go traffic this evening I get within 2 redlights of my on ramp to I-75....I cant wait

I am almost there! Home Free!
I come to that 2nd to last light and whoa! brake pedal to the floor and I barely got her stopped. I was so glad I was stopping slowly and not slamming on the brakes. I pull off into the gas station parking lot and start pumping them. absolutely NO resistance

Straight to the floor.
Since I was so close to the open freeway I eased back out into traffic and creeped down the road with my hazards on. I knew I could get her home due to fast moving traffic on 75 at this point. I made it the 20 miles home and did not touch the pedal once until my exit. I prayed..I applied.. and what do ya know....TOTALLY back to normal. Excellent feel and stopping power. 100% back to normal. I even ran a few errands around town late tonight and they seem as if nothing ever happened..
What the hell happened? I would rather get a jump start on this before it goes completely out.. you know?
I did noticed this week a squealing sound has started at start up... warm or cold.. like a squealing belt but I cant tell what/where its coming from. Related maybe?
Thanks guys in advance. The Town car has not been getting the thumbs up like my 240d....I mean I get at least 3 compliments everyday in the 240...Its gotta be the hubcaps!