I have had bouts of sciatica and plantar fascitis (tendonitis in the foot) over the past 2 years, and have found yoga and regular walking the best defense. This won't help anybody who is going next week, but if you are planning ahead for next year, start now! There are a number of stretches that will limber up your feet, help arthritis, and get you ready that you can learn in a Yoga class. Also, if you try to get used to a couple of miles of walking every day, you'll feel much better when you walk 5 plus miles each day at WDW.
And the hot tub is a Godsend!!!