Conversation:

One thing I have noticed is that nettle stings seem to hurt a lot less when I am manually working when I get stung. However once I stop working a rest they start to sting a bit about half an hour later.

Any idea why that is?

Personally I find that any sort of pain is much worse once you sit still and think about it. I don't always feel it when I get stung when doing the gardening, then suddenly notice it later.