Those caught napping are not affected by this! (8)

I believe the answer is:

insomnia

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'those caught napping are not affected by this' is the definition.
The definition suggests a singular noun which matches the answer.

This is all the clue.

Can you help me to learn more?

(Other definitions for insomnia that I've seen before include "In restless state" , "Wakefulness" , "State of chronic sleeplessness" , "problem at night" , "Sleep disorder" .)

I've seen this clue in The Irish News.

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