Case of happy individual dropping off son, wildly excited (5)

I believe the answer is:

hyper

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'excited' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for hyper that I've seen before include "Unusually energetic" , "More excitable than normal" , "Slang adjective for over-active or highly-strung" , "Prefix meaning excessively, perhaps active" , "Over-stimulated" .)

I've seen this clue in The Times.

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