It sounds like a leak somewhere - first thing to check is the brake fluid reservoir level to see if it has dropped at all?
I had a problem not dis-similar to this but slightly different in my old Corolla AE86 - I got some "mechanics" to do me a brake job as a "homer". When I drove off - after the work has been done, down a very steep hill - and hit the brakes, nothing happened apart from the pedal going to the floor..
Went back to their house and almost battered the two idiots (a father & son) when they said they forgot to tell me that my master cylinder had failed.
The actual problem was that they had fitted brake pads that didn't actually fit properly and would not move against the brake discs. You wouldn't expect that to cause the pedal to go all the way to the floor, however, that was the cause - once the brake pads were changed (by myself) all was well in AE86 driftland
I've done all my own work on cars since that fateful day!