Nostalgia seems not to need hospital treatment (12)

I believe the answer is:

homesickness

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'nostalgia' is the definition.
(homesickness is a kind of nostalgia)

I don't understand the remainder of the clue.

(Other definitions for homesickness that I've seen before include "Sadness when away" , "Feeling of missing one's place of residence" .)

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

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