I would be concerned that it might be Oak Wilt, a very quick hitting fungal disease. The problem tends to begin with wilting at the top of the tree and quickly progresses through the tree, and can kill a mature tree in just weeks. The only way to diagnose it with certainty would be to either have a certified arborist look at the tree or take a branch that is showing symptoms to your county extension office and have them send it to PSU Plant Pathology for analysis.
If it is Oak Wilt, the biggest concern would be saving surrounding oaks.
More about Oak Wilt can be found here: