Spider bite/bee stings have reduced inswelling (but definitly not itching) and are beginning to resemble a small zit or welding spark burn. (white head with clear fluid).

I think it was a hornet. It wouldnt be the first time this winter I found one upstairs. The attic is full of nests.
Well off to the shop. Weather sucks but I'll be able to start it up and pull it outside.