If you use a grounding mat living on the 19th floor of a high rise apartment with 100’s of apartments sharing the same power grid
You’re basically trusting the wiring of that building.
I wouldn’t.
Discussion
Any appliance in this building can rise the charge on ground so this seems useless. Would need your own ground not connected to anything else and shielded against everything in the cable trays. Maybe using water pipes as ground wire could work in this scenario.
I did try using a grounding mat in my apartment plugging it into the wall socket. It felt wrong right away. I could feel tension building up from my feet and felt drained. Turned out to be a waste of money.