Nocebo has measurable negative effects: it is the opposite of the placebo effect. Nocebo is health problems or a worsening of symptoms, solely due to the conscious or subconscious expectation of harm.
Highly relevant to Covid vaccinations because subconsciously a lot of people fear side effects, so perhaps many anecdotal side effects are purely psychosomatic. I think psychosomatic symptoms are still truely harmful: few people can just decide to think themselves better.
