If we are low on electrical storage or production our individual systems will accordingly be subpar at function ( and we have pain).
Earthing in simple terms is the adding of electrons (the EM Field) from the earth's large EMF, thru connecting with the ground.
People can be dramatic, exaggerate and associate many attributes to many of the natural living treatments and ideologies, when they are often merely simple adjuncts which may have great ability in assisting and synergizing our other natural realignment work as well as the bodies natural processes which attempt to do that, tho we often work at cross purposes to it w our life style choices.
Simple in comparison to regular medicines usually more sophisticated medicines and tecniques which often have involved and or detrimental side effects and often work at replacing body processes rather than accentuating or restoring their power.
Our bodies are running on electricity(the primary energy source (*) not disregarded, just not germane here) more than they are running on food or food constituents. Take away food, the body will still run. Take away electricity, the body stops running at all.(this is how and why people can be more energized after 40 or more days of no food)
The food we eat doesn't actually feed our bodies organs or the organs activities or actual cell tissue, it feeds the electricity creating factories in our cells. These mitochondrial electricity factories take the deconstructed food (glucose or fat), mix it with oxygen and burn the mixture to make electro chems/ EMF's, so that the cells, singly and together can work at being a multi system system, known as a human body. (our mitochondria can also produce the chemical electricity by the cells producing a burnable fuel from fermenting glucose and or lactic acid if oxygen isn't available. This is what cancer cells do).
It may seem this is being smug or even ridiculous but the point is that it is electrons that we need and use and any way we can acquire them will produce or assist the beneficial results of a normal running body. But not specifics for any one system unless that system's cells are already lacking in EMF fuel.
Earthing may provoke any number of experiences, mental or physical in our body, if we are already running at an electrical sub normal state, but whatever is provoked is a normal procedure brought on by a bodies systems using the added E Fields to run cells function and tasking not by earthing EMF's "per se" as if by "magic" into our body.
So the benefit can be exaggerated by being misunderstood and it can be accused of causing, as you mentioned a negative response, that if correctly associated was again an example of our experiencing a reaction to our body systems normal tasking of some kind, perhaps negative due to a lack of the proper or enough raw materials your body has been ingesting. If we are low on tissue building or chemical creating materials we frustrate the electricity running cells and organs using the raw materials to process them as needed into hormones, proteins, ect.
How about a glass of a complete food, like raw whole milk? or as Mallow has been mentioning B6 or Iodine
or or or (raw material), (and don't neglect to consider the implications of our Intestinal Flora's importance in our whole bodies systems functioning well and how agri bizes use of herbicides destroys that floral population(and creates, toxic/diseased neurology, 'leaky gut' which further congests and taxes our fluid systems, ect ect) and thus further complicates the work the electricity eating cells are trying to accomplish and we are trying to assist by earthing.