Being unable to sleep, I rebuilt mansion (8)

I believe the answer is:

insomnia

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'being unable to sleep' is the definition.
I can't judge whether this definition defines the answer.

'i rebuilt mansion' is the wordplay.
'rebuilt' is an anagram indicator.
'mansion' anagrammed gives 'nsomnia'.
'i'+'nsomnia'='INSOMNIA'

Can you help me to learn more?

(Other definitions for insomnia that I've seen before include "problem at night" , "Not getting off" , "Sleep disorder" , "Condition affecting sleep" , "In restless state" .)

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