Brake Master Cylinder problems of the 2009 Dodge Challenger

This car is not frequently driven and serves as a sports car only, not a commuter, it only has 025,379 miles on it. It's a six speed manual trans with clutch pedal. While driving the car noticed what felt like brakes (all of them) dragging, increasing the load against the clutch and throttle. Not extremely but enough to notice. This seemed to be getting worse and I was concerned about a malfunction with computer override features like "hill-assist" and "stability control", both I generally switch off. After about 20 minutes of driving slow surface street speeds, stop & go, I came to a stop sign and the brake pedal went to the floor. The car did slowly stop. I was "on alert" and was using the gears to slow anticipating a possible failure. We were going to dinner and after about 4 more pedal to floor stops, it was parked for just over an hour and regained it's brake pedal pressure after sitting. I cautiously drove straight home. There were no warning lights on the dash of any type at anytime. I think this indicates some computer or other system failure connected with this. Conditions were a 90 plus degree day with the a/c-on. Things seemed hot under the hood and around the master cylinder and reservoir when I first parked for that hour. Other than "no warnings", the other significant fact is, neither of us smelled overheated brake materials as you typically would. This I find really odd because if it wasn't the brakes dragging on the car, why did they fail and go to the floor "while hot" ? as it is my habit at all times, I pulled the parking brake release a lot, assuring it was off through this. It's in working order and holds the car when I pressed it's pedal down, clicking and locking it to do so. I know of others who have had weird brake failures with other year model Challengers. Please check on this ! thank you for your time.