if its the hydraulics sometimes pumping the clutch can give you a bit movement on the slave cylinder and free the clutch.
But I had something similar, changed the clutch master and slave cylinder but still had problems. I found all the pivot points (clutch pedal, pivot between pedal and cylinder etc) were worn. I repaired, replaced all these points, reduced the amount of free play and got back to a good working clutch. just a build up of wear over 50 years!
mike