Hydrangea with black stems

Hi,

I was hoping to get some advice with regards to my hydrangea. I have just returned from a weekend away and my potted hydrangea had been blown on its side. When I pulled it up I noticed that all of its stems have turned black and are all very limp.

Does anyone know what the problem is or what may have caused it? Also, is there anyway to reverse it?

Many thank in advance