Only a guess as I had similar yrs ago.
(a) Cable operated clutch has pedal return spring that may have come loose or broke.
(b) If a hydraulic check fluid reservoir under bonnet look in book to pick correct one. if low top it up to level.
(b2) May be air sucked in to system via leaking master cylinder /slave cylinder. Replace the cylinder/s.
(c) Worst scenario and most costly is the clutch is on its way out. Some mechanics say to test. Apply hand break, engage 2nd gear try pulling away gently if car stalls its not clutch. If it tries to move its very unlikely it needs changing at this time. If the engine on more revs still runs on the clutch is almost shot and will likely suddenly start slipping badly.
bob
August 2013