One day I'm feeling fine - able to work and play and plan. The next day I am achy and whiny and grouchy and tired - barely able to get out of my own way. What is it?
The common cold... a sinus infection... a runny nose... sinus headache... fever... and I'm done for.
How can a microscopic organism knock the stuffing out of a complex, intelligent being like me? My eyes are watering. My nose is threatening to drip. My sneezing is a wind shear danger to low flying aircraft.
Ow! I'm ready to be better now! Ow!