Really, why couldn't he get up?

This morning as I carried Zozer through the rain into school, we sang together:

It's raining, it's pouring
The old man is snoring
Bumped his head and went to bed
And couldn't get up in the morning!

Whereby we then had this conversation:

"Mommy, why couldn't he get up in the morning?"
"I don't know. Maybe because he bumped his head."
"Well, you can bump your head and still get up in the morning."
(The "duh!" was heavily implied.)

I didn't have an answer. Anyone know?