The Expanding Knee's

Okay...anybody else here work in retail? If so...do you have the trick to prevent your knee's from swelling up after standing in heels?! I've only been making it for 4 hours standing in my heels and then I've been switching into my flats for the other 4 hours, but now I'm home...getting ready for bed and my knees are so swollen that I can hardly bend them. Hopefully it goes down before tomorrow!!! But I'll be in my flats...ALL day!

Needless to say...if you have a trick...please let me know!!