My friends need something to tease me about on any given day and one of the opportunities I provide (other than my water kefir "still") is that I like to walk around barefoot (in the absence of extreme cold or heat.)
I've actually burned my feet here in southern Nevada a few times by under-estimating just how hot the sand/gravel were getting. Anyhow, none of them are ever seen without shoes even inside while I am barefoot unless I'm walking outside or away from home.
I've also scandalized them a few times by sitting cross-legged on the sand/gravel rather than joining them at the picnic table or in a chair. But seriously, it DOES feel good to me to be in contact with the Earth whether it's the sand/gravel here, the red clay when I lived in West Virginia or the black soil of Massachusetts and Wisconsin.
On grass, I like to lie flat on my belly and rest my cheek on my arms. Unfortunately, I tend to itch when I get up but I still do it at times.
I don't know about negative ions or parasympathetic processes, etc., but I know I like "earthing" which I always called "sitting/walking/sprawling." :-))