system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are people able to think themselves sick? (somatoform disorder)
gpt
We don't feel sick because we are sick: we feel sick because certain patterns of neurons in the brain fire. Most of the time, they are firing because we are sick, but not always; and doctors aren't sure why they fire when we aren't sick.

And the real answer is "we don't know". In many ways, somatoform disorders are the evil twin of placebo effects; and we really don't understand *how* or *why* either work, we just know that they *do*.