Hello, I used to wake up with really sore feet when I was suffering from really bad PMT - I guess this could be something similar. I found it (and all the water retention problems) went away once I started eating a low GI diet!

Also it's possible to get leg cramps in the middle of the night (esp if you are low in calcium and magnesium) - do you think you might have had cramps in the night and not woken up?