Ouch, Jadey!
We were to to never use a cold bag. We've even discussed how to heat a bag when there is no power available.
How did you do that??
One method was to put the bag on the dashboard of a car which is in the sun. Of course, if I ever have a power blackout there won't be any sunshine about.
Another way was to wrap a bag in a hot towel - I haven't quite worked out how I manage to heat the towel with no electricity, but I'm still working on that one.
My current idea is to take a bag to bed when I have a snooze and snuggle it.