I can think of a few possible explanations, but nothing definitive. Do you have allergy problems? Allergens have been bad around here this year and a couple of times have caused off days. Perhaps you are coming down with something or are overtrained. Maybe you need to back off for a few days to give yourself some rest. Are these hills you normally ride without these issues? If not a hill harder than what you're used to can easily cause that reaction. Just some thoughts........
Dan