Mental illness and "serious leves of emotional stress" is pretty common in fiction, but I think anxiety disorders specifically have been pretty rare until this year. Pomni, Kobeni, and Peppino from Pizza Tower all have very similar things going on with them, and I don't remember seeing that kind of thing... pretty much ever before 2023 (except for the Chainsawman manga).
If you or someone know of earlier depictions of this anxiety disorder in anime/gaming before than, please let me know though - I like these kind of characters and would also rather know if I'm wrong about this.
EDIT: forgot about Bocchi, she also fits into this category somewhat.