What kind of hydrangea? Where are you located? What has your weather been like in the past three weeks? How have you been watering? What's changed since last year? Other than wilting what else is going on? Did you check for insects on the top and the underside of leaves? Tap a leaf over white paper and see any insects? Has the soil become compacted due to foot traffic?
All this inforamtion would be helpful to determine if it is a disease or pest or even something mechanical.