Why do we say “fast” asleep? Can you be slow asleep?
Most definitly. 
From the Straight Dope Mailbag:
Where did we come up with the expression “fast asleep”?
Because the opposite of fast is fast. From dictionary.com:
Noses run and feet smell.
Goods sent by water are a car-go. Goods sent by land are a ship-ment.
I gather you’ve never had to learn to march in formation. If you found “fast asleep” puzzling you’d really be baffled by “stand fast”.
And we drive on a parkway and park on a driveway. But so what? :rolleyes:
When you eat in a restaraunt In England, you are given a bill and you pay with a cheque. In America you are given a check and you pay with a bill.
Actually, I am generally brought a tab and pay with a card (unless my wife drinks the Tab, although that is rarer since the advent of Diet Coke).
(the obligatory Yakov Smirnov post)
In England you eat in restaurant. In Russia restaurant eats you!
“Hold fast” means “stay where you are.” In old timey sailors’ jargon, it got compressed a bit. When a movie pirate says, “Avast, ye swab!” he means, “Hold it right there, you low-ranking mopper-of-decks.”
A holdfast is the root-like structure that keeps kelp in place. 