Day-to-day symptoms can vary, as others have said.
Stuff like sensory overload, anxiety level, and capacity for prolonged social attention are sometimes good and sometimes bad.
However, someone I've lived with for a number of years has noticed that I also seem to have longer, over-arching phases of "good" and "bad" days. They've said that I will seem to be doing better for a number of months... seeming more organized, less plagued by sensory issues, better able to hold a conversation and respond to emotions. Then I seem to spiral the other direction for a few months, where everything is a source of frustration and irritation for me, I withdraw further into myself than I already was, I have problems with anger management, and so forth.
So I definitely agree with the presence of the good/bad days phenomenon. How it plays out seems to be a highly individual issue, depending on their environment and circumstances and neurology.
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Plantae/Magnoliophyta/Magnoliopsida/Fabales/Fabaceae/Mimosoideae/Acacia