Can you please explain what seratonin syndrome is, particularly (like the above hypnosis / nlp split) where the edge of medical literature is? Highly interested

Can you please explain what seratonin syndrome is, particularly (like the above hypnosis / nlp split) where the edge of medical literature is? Highly interested, however for some reason was previously inclided to believe the phenomenon did not exist, akin to how adrenal fatigue can't be proven.