Dora has agreed to go skydiving with her boyfriend to help him celebrate his 30th birthday, but she is absolutely terrified to do so. The morning of the big jump she wakes up and reports that she cannot feel or move her feet. She is upset by this, and her boyfriend takes her to the hospital. Doctors in the emergency room cannot find anything physically wrong with her. After the time for the sky-dive has passed, Dora's feeling of her feet seems to return without explanation. This could be an example of _______________.