Psychogenic illness, and The Placebo Effect, should be mandatory in every high school biology class.

We still want people to go to the doctor (or at least an NP) when they think they might be sick. Making this a big point of emphasis in a non-selective educational setting would probably harm overall public health. It could be discussed in psychology classes, because everyone attending is assumed to be capable of discussing that topic.

How exactly do you justify this? If mass psychogenic illnesses were so easy to instantiate, they would be extremely common. That's just not how the world works.