When I was a very small kid, we had those rubber jobbies on our taps that let you swish water round the sink, but if a tap wasn’t quite turned off dripping water used to collect inside, until it finally ran out, what I called ‘ribbling’ because of the noise. One evening the hot tap did that all across the back of my hand. I created quite a fuss, my mum told me not to be a baby, it wasn’t hot.
Well, I slept with my hand between the two mattresses because it was the only way I could stop the burning sensation, the next morning the back of my hand was one large blister with the skin already starting to peel!
If I was you I’d be off to A&E, but first I’d be wrapping cling film, or at least a dry bandage around it to protect it, that could be rather nasty otherwise.