precarious sleeping

[mengta]

Precarious sleeping, those Elizabethan nights were, when beds were kept from sagging with a rope strung around the mattress. This, our guide tells us, was the origin of, "Good night, sleep tight."

What does the first sentence mean?
Is the "sleeping" here a noun or adjective?

thanks

[J-P]

verb.... carefully sleeping... sleeping dangerously....

[Tdol]

I'd say a gerund.

[mengta]

now i understand the sentence better.
but i have another question, why is it "precarious" rather than "precariously" here?

thanks

[Tdol]

In my interpretation, a gerund would be modified by an adjective not an adverb. The nights weren't sleeping- people did that. However, the act of sleeping was precarious because it was dangerous.