If you're going crazy, you at least have company.
I know exactly what you're talking about. It's a hot, dry, strange smell. I think it's a pH phenomenon traceable to environment and my body chemistry.
I suppose it's also possible that I see or hear something that triggers an olfactory memory, but I don't think that it is, because the trigger is never found, and because I am much more likely to smell something and have a subsequent memory than to see or hear something and then
recall a smell.