Those were a medically certifiable illness or a death in the student's immediate family.
A 'smart' student in the back of the classroom waved his hand and spoke up. "But what about extreme sexual exhaustion, professor?"
As you would expect, the class exploded in laughter. When the students had finally settled down, the professor froze the young man with a glaring look.
"Well," he responded, "I guess you'll just have to learn to write with your other hand."