I understand, OP. I actually find the science/social anthropology behind human social interaction and cues like non-verbal behaviour more interesting than using it myself, lol. So no matter how much I learn about what you should when 'x', and why you shouldn't do 'y', it is all just knowledge to me, theory, if you like it. Mainly because it's not innate and also because in certain cases, I don't understand why and frankly, don't actually care. I find it a sometimes amusing mixed bag - I occasionally want to know these things that seem to so second nature to others to not create misunderstandings and awkwardness, but then with certain social niceties, I couldn't give a toss, to be blunt.
And to touch on the whole stress/depression/anxiety element: Do I sometimes miss/ mess up social cues because of anxiety? Probably some of the time, yes. But then again, I managed to do something socially inappropriate in the comfort of my own home, where I feel the safest and least stressed. Something that completely passed me by and unbeknownst to me ruffled literally everyone else in the house. And it's hard because I half want these things to be pointed out, especially if I hurt feelings, and half don't because it makes me feel like rubbish.