If you didn't have an abrupt temperature drop (frost or freeze) in the last couple of nights, the only other thing that might affect the whole tree like that would be an overspray of some weed killer. Any neighbors spraying their weeds around you lately? Windy weather?
Have you asked your neighbors if anyone else's trees have been affected?
Have you had enough rain, or watered the tree in the last few days? Maybe spray down the whole tree with water tomorrow and see if that helps? Then give it a good deep watering if the soil is really dry.
