Anyone in science will miss this, but to their defense, it’s nearly incomprehensible. It seems like a concept difficult to transmit in words, but to me it sounds like you are describing some sort of non-human external pathogen that replicates/propagates within you, evades the immune system, and uses novel communication systems to cause symptoms and perhaps measurable abnormalities…and such a pathogen has co-evolved with hominids and in some fashion responds to chemicals some plants make to defend themselves.

The idea seems plausible. But hard to test. Or at least hard to come up with a specific testable hypothesis based on this idea. But it does seem like something we should expect in nature. And viruses fit at least part of the picture.