Answer: It doesn't sound good for your oak tree! What you describe sounds like oak wilt but of course I can't diagnose it positively without seeing the tree. However, I found a publication with photos that will enable you to compare the leaves of your tree to the leaves of a diseased oak. This way you can confirm or rule out the posibilty of wilt. Here's the web address of the publication: http://www.extension.iastate.edu/Publications/SUL15.pdf
I hope it is helpful.
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