Actually, my father and I plan on building one such tank in our allocated "meditation room" (The joys of building a custom home--aside from paying for it until you're dead (IMG:
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The only damage I've heard of done from sensory deprevation comes from being driven insane--since one has no concept of physical orientation any longer.
Kind of like how locking a person in a lighted room, with no clocks or windows to base relative time off. Allegedly, they go nuts.
I forget the name of the study done on this--back when ethics in human expermentation was less than strict.