Quick Clutch Question

Hey All,
 
Just had a quick question for you all about my Sw20. I took her down to Tenterfield in January and took my cousin for a drive through the mountains out there. It was a particularly hot day and about an hour into the drive, we turned around to head back up the mountains. As I started getting into the twisty sections I started to notice my clutch getting more and more play but the bite still being exactly where it should be. It seemed that if I kept changing gears frequently, it would keep working normally, as soon I sat in a gear for a while it would loosen up again until finally, I lost the clutch completely. So I nursed it back home on the highway and by the time I got home, the clutch had come back! I opened the frunk and had a look at the clutch fluid level, it was overfull and some had leaked out of the cap. Not too much but maybe a teaspoon of it. I left it over night and fired her up in the morning and all was good. Drove it all the way home and it's been about a month of driving and it hasn't played up. Just wondering what could have caused this so I can prevent it from happening again?
 
Cheers,
Graham