I have 215,000 miles on my everyday ride.
Last night I was coming home from work and 2 deer ran in front of me, slammed on the brakes and managed to avoid deer.
Right afterwords my brake light came on (not the ABS light) and message on dash saying "Service brake system". Ok I thought to myself until I went to make a turn and realised that my brake pedal went to the floor and I wasn't slowing down as quick as I wanted to. Pumping pedal helped but not much.

Since I was on lightly traveled back roads I slowed down and managed to get home a little later than usual.

This morning I checked brake fluid and it was where it should be, I changed pads and rotors March a year ago and have had no issues.
Although this past winter I would have the ABS light come on but would go off within minutes after engine completely coming up to operating temp. I just attributed it to the bitter cold we were having.

If I have ample fluid what are the some of the possibilities of the pedal going to the floor??

 

If you are not losing fluid and all 4 wheels are affected, I would be looking 1st at the master cylinder

 

I know where it is but what exactly would I be looking for and how would I determine that this is the problem.