What can I do to get over my irrational fear?

Ever since my grandfather tragically got run over by a parade float driven by a guy dressed up as Santa Claus, I have had a terrible fear of Santa. All year long I dread Christmas because I can't go anywhere without running into someone dressed as Santa Claus and triggering a panic attack. Even seeing a Christmas special on TV can cause sweating and hyperventilating. From September until December I can barely leave my house without ending up in the emergency room. What should I do?