The Red Baron was ill too. He was having terrible headaches from an earlier wound to the head.
Some people have wondered if it even affected his judgement on that fateful day, because the way he chased Roy Brown's (nephew?) was rather uncharacteristic of him, allowing himself to be drawn close to the ground, and prolonging a fight by chasing down an enemy fighter. For one, he even had Roy on his tail.
The Baron's motto was a quick kill, fly in quickly, possibly from above, and get out fast.
Erich Hartmann followed that rule a lot too.