To me it just feels like someone rubbing a sunburn.
But the longest I've ever gone was about 2 hours. Enough to get annoying, but it tends to kind of numb itself after awhile.
A friend of mine that was in my platoon was in a bad car wreck and received a pretty gnarly scar due to it.
He got a tattoo of a knife cutting his skin on the scar. It was pretty neat. Wish I had a picture of it.