It is related to the energetic fields in the earth. I don't have a good reference for this but wikipedia takes a swipe at it.
Geopathic theory - Wikipedia, the free encyclopedia
I think trying to create a high level explanation can make stuff sound more woo-woo than it is. To me it is about earth energy making a space less than 100% supportive for people, plants, and animals. Once the energy is re-routed or dispersed, the space can be fully supportive again. I don't know if barometic pressure interacts with geopathic energy.
Here's another link:
Geopathic Stress - The effects it has on your health, and how to counteract it..