Brake problem today

Hello all,
I was driving in very slow traffic today and I had the AC going full blast. The temp outside hit about 117 today. My water temp started to rise a little bit, which is normal for those conditions. I'm hopin someone can explain what happened next. My brakes started to give out. I could push the pedal half way down before I felt any resistance, then I could push it down to the floor easily. They weren't just spongy through the normal range, half the range was totally free moving, no resistance. At first I chalked it up to the heat and the stock brake lines. Can anyone confirm or deny? I let the car cool down for a few hours before driving home and they felt a little better but got progressively worse as I went home and the temp went up. Any advice?

Thanks,
Mac

I was in slow traffic, so I wasn't using the brakes to the point of boiling the fluid from the caliper up, or cracking the rotor, but it was hot out, 115+ degrees. I believe the engine heat and Phoenix temps had something to do with it. Is that possible? Now my brakes work fine as they did before. Do you think it was just the heat or do you still think I might have a bad m/c? I think if the m/c was bad it would still be showing poor performance. How about you?

I just got the car 5-6 months ago. Don't know if it was changed before that. I'll change it and let you know if it happens again. Of course, the only way to really check it is a good romp in the canyons. That should be fun.