Dreamer relied on performance without energy (5)

I believe the answer is:

idler

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'dreamer' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?

I can't explain the remainder of the clue.

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(Other definitions for idler that I've seen before include "Lazy person" , "Do-nothing" , "One does little" , "Not working so hard" , "Lazy type" .)

I've seen this clue in The Daily Express.

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