Background: Native English speaker here. I grew up in India, but have lived most of my life in the United States. My fellow Americans often comment upon "Britishisms" in my usage. For example, I tend to spell the color "grey" rather than "gray", and I use "quite good" to mean "satisfactory, or perhaps better" rather than "excellent".
The sitch: Today I told a friend that I "wasn't all that shot in the head" about a particular book. My friend, US born and raised, said he'd never heard the expression before and asked what it meant. I explained that it meant that I didn't find the book all that engaging and wouldn't be enthusiastic about it. My friend and I then proceeded to google the expression, but a search for "shot in the head" merely brings up page after depressing page about school shootings.
The question: is "not shot in the head" a common expression to express lack of enthusiasm? I've used it on occasion before, including in conversation with my late spouse, and heretofore have never had to explain it to anyone. But the fact that I couldn't find any relevant results on the Goog (not even when I looked at ngrams) is leading me to wonder whether the idiom actually exists. An actual source (textual or video) where this expression is used would constitute great evidence, but I'd settle for an answer like "yes, my grandmother from New Zealand used to say it".
If this question is met by resounding silence (or a chorus of "never heard it ever" in the comments), I'll assume that I must have misheard something years ago and have been perpetrating a catachresis for much of my life. Thanks!