crew probably died of their own insane actions long before any physical pathology. The physical distortions might have led to death eventually. What McCoy did was come up with a "pain killer" to numb the fun house mirror sensations—temporarily.
Gravity boots? No mention of that in TOS. Anyway, since the Enterprise
sensors could not detect the Defiant
, it might have been some kind of mirage. I think the environment suits were a wise precaution. They might have been beaming into space. The ship appeared to have power, although the air might have leeched away. McCoy passed his hand through a table and one of the corpses. I always figured that the air was intact, and McCoy had wandered down to a threshold between the universes.
To coin a phrase, "'brane and 'brane! What is 'brane?"