Brake Master Cylinder problems of the 2012 Chevrolet Sonic

I was driving down the street (straight and flat, no turns or hills) at 25 mph and went to use my brakes. To my surprise there was no power assist. The car only has 48k miles on it and had never displayed braking problems prior to this incident. The car did not have issues at the stop sign just a block before. As it happened a few blocks from my house, I drove it home and parked it. Besides the lack of power assist, the motor started to idle rough-- it would surge to 2500 rpm and then slow down to 700 rpm, all with no throttle input. When I popped the hood, to look for an obvious loose hose, I did not see anything that looked out of the norm. However, there was quite a bit more noise than normal-- it was a combination of hissing and whirring. Not the normal sound the engine would make while running with the hood open. There were some noises coming from the brake booster area (driver's side by the firewall) that I had never heard prior to that day. The car has a 1. 8 four cylinder and a 5 speed manual. The issues did not impact the clutch pedal in any way, so I doubt it is the master cylinder. As I noted it seems to be a brake booster issue. . . However, I have not been able to get it to a garage yet as the issue just happened. (I am no mechanic, but have a decent understanding of how cars work. ) either way, it was quite a surprise. While I am a male in good physical shape, even I needed to stand on the brakes to get the car to slow down from only 25 mph-- had I been going faster, I would have likely needed to use the e-brake to slow the car. Again, at this time the car has not been repaired, but the issue happened just yesterday. For what it is worth, the temperature was cold at the time of the incident (15 f), but there was no snow or ice on the road, and it was sunny out.