1992 Nissan Sentra

I recently bought a 1992 Nissan Sentra, after some routine maintanance the car was running great.I was starting to enjoy my new used car. Then, after driving to work and driving home with no issues I started having problems with my cluch when I went to the store later that day. The car was fine when I turned it off but when I left to got to the store my clutch petal had no back pressure and did not engage untill almost to the floor. I was still able to drive the car but practically had to pop the clutch to get going. The clutch petal will stay almost down to the floor until a bump unsticks it when it will pop backi up. but when I go to engage it again, no back pressure until almost to the floor. What could have caused this to happen so suddenly.