Back when Lex was in the Golden core realm, much of his survivability depended on his core. Even if his body were turned to mush, as long as his core was unharmed, his energy would be able to flow, and help him recover to his peak state.
This was as a result of the unique blend of his body, soul and spirit. His new form of existence had the benefits of all three, with the only drawback being that more energy would be required to carry out the functions of any one.
For example, his body, even as a mortal, had the inherent ability to heal. Souls and spirits all lacked that, though both of those boasted a certain durability in their own way. But bodies did not necessarily always heal completely the way they were before injury, yet souls had an inclination to return to their whole being.
