Welcome to the forum Diane!
First thing - breath - don't panic!
Do you know what variety of hydrangea it is? There should be a tag on it to tell you what it is. Some hydrangeas are hardier than others.
My first thought though is that no, you have not killed it. You have given it quite a shock though!
To help it recover, first put it somewhere where it will stay at a warm constant temperature, with lots of light. Trim off all of the dead or dying flowers. (don't worry, it will flower again!) Keep it watered, but not water logged, and let it re-cuperate. You could give it a drink of alfalfa tea for a bit of a boost if you are so inclined (recipe in either Rose Care Forum or Organic Forum). You will no doubt lose some of the leaves as well, remove them when they begin to die.
Soon, though, you will see it begin to turn around and grow again.
Get back to us with which type of hydrangea it is and we can be more exact for you though.
Feel free to return with any other questions, or just to chat anytime!
Relax! It will be okay!