All the symptoms suggest the clutch master cylinder piston or fluid is not returning smoothly. A strip and overhaul will doubtless provide the reason.
When a heavy footed gent operated mine whilst on a rolling road it was left with a lot of pedal return play although clutch action not effected. At first I suspected a broken external pedal return spring but there isn't one on my car. In any case by the end of the 50 odd mile return journey it had corrected itself. Can only assume the extraordinary travel placed on clutch pedal had left the m/cylinder return spring coils jammed temporarily. Not happened since
