Daydreamer who is easily disturbed? (5,7)

I believe the answer is:

light sleeper

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'is easily disturbed?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'day-dreamer' is the wordplay.
'day' becomes 'light' (I've seen this in other clues).
'dreamer' becomes 'sleeper' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'light'+'sleeper'='LIGHT SLEEPER'

'who' acts as a link.

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I've seen this clue in The Globe and Mail.

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