"fell into a deep sleep" vs. "fell into a profound sleep"

[Niki]

English Language Tests, Intermediate level

ESL/EFL Test #28 "The Hare and the Tortoise", question 7

It wasn't long before the hare fell into a ......... sleep.

(a) profound
(b) steep
(c) deep
(d) full

English Language Tests, Intermediate level

ESL/EFL Test #28 "The Hare and the Tortoise", answer 7

It wasn't long before the hare fell into a deep sleep.

Correct answer: (c) deep

Your answer was: incorrect
It wasn't long before the hare fell into a profound sleep.
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Why "fell into a deep sleep" and not "fell into a profound sleep"?
Google can find 14.600 examples of "fell into a profound sleep", what's wrong with "profound sleep"?

Thank you in advance.
Niki

[Alan]

Hi,

To me 'prfound' has the idea of 'deep' in an intellectual sense.

A
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