Meridians are an interesting example of a demon associated with the cycle of nature, specifically with summer heat and field work. In many cultures there are similar characters that perpetuate the fear of natural forces. As for experiences, I've heard stories of people who experienced strange fainting spells, headaches, and even had the sensation of someone invisible tugging or pushing them in the fields at noon.

@czulu Remember that in the old days people had limited medical knowledge. Today we know that sunstroke or dehydration can produce similar symptoms. But for the ancestors it was something unexplainable, so they attributed it to the action of demons.