How can a noun be countable and uncountable at the same time?
For example 'shock'.
You can get a shock.
I'm suffering from __ shock.
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People talk a lot about countable and uncountable nouns, but this is really a misnomer. Countability is not a property of a noun that might be similar to gender in other languages. Rather, it is a property of the sense.
Consider water. The sense that denotes the substance is uncountable: I'd like some water please; I'd like a glass of water. But the sense that denotes a packaged quantity of water is countable: I'd like an apple, a banana, and two waters, please.
Consider your example, shock. One sense denotes a discrete incident of surprise or electrical stimulation. This is countable: I touched the wire and got a shock; a tree fell in the yard, which was certainly a shock. Another sense denotes a state of mind: After the cat jumped on my head, I was in shock for a few minutes.
English can be capricious. For example, "He drank water," uses *water as an uncountable noun.
From Wikipedia: "The Meeting of Waters... is the confluence between the dark (blackwater) Rio Negro and the pale sandy-colored (whitewater) Amazon River." Here, the two rivers are two waters, i.e., countable.
More peculiar yet: "He caught ten fish, salmon," shows fish as uncountable. "He caught two fishes, a salmon and a trout," uses fish as a countable noun.
Again, "pour wine," uncountable; "serving fine wines," i.e., of different types, countable.
English Club gives more examples.
There's no accounting for the innumerable idiosyncrasies of English.