What Bit/Stung Me

Today I was breaking off a tree branch to feed to the goats. I saw a light brown spot on the back of a leaf but thought nothing of it. Afterwards I felt severe stinging/burning on two fingers of my left hand. Soaked the fingers in ice water while watching tv. Few minutes later something fell out of my hair onto my neck and stung me real good. Brushed it off onto the floor (luckily it didn't sting that hand)and saw it was an asp (puss moth caterpillar). That was around noon and my neck still hurts, is swollen and red. Felt nauseated this afternoon. Fingers are fine now. We've lived here six years and have never seen one here before.