In a general context of health, the Devil represents the unhealthy aspects of your surroundings. Diseases and injuries that originate from factors in the physical world. Things that are physical, material and materialistic. In a wellness tarot reading context, the Devil can represent addictions.
Devil tarot card is often associated with the Devil signs. These can be anything that is a symbol of excess of various kinds. This can be for example a substance or behavior you have that you overdo. This can lead to a physical or psychological problem. The Devil can also point to a loss of psychic abilities.