Plantar fasciitis, perhaps?

If that's the case, supportive shoes and stretching can help. But I think plantar fasciitis pain tends to be on the front end of the heel. Disney involves so much walking that, in my opinion, it would be worth getting a medical diagnosis. I would rather have a doctor say I came in unnecessarily than get to Disney and have the pain get worse. No matter what, footwear choice is important for a WDW vacation!