Thanks for that information 

Soul leaving syndrome is the direct translation of 离魂症. As funny as it sounds, that's an ancient way of calling such syndrome. Modern term should be hypotermia, leading to unconsciousness and hallucination, and yes, it will lead to death. And when he hallucinates under such circumstances, he will see all his childhood trauma.
This is why XW is so afraid of cold.

 Xtinew:

I believed it calls PTSD (Post st-traumatic stress disorder) is a mental disorder that develops in some people who have experienced a shocking, scary, or dangerous event. This's not just affecting military combat service  members but also anyone, just like what Xie Wei experienced in young age.

This sounds like a better explanation.  Was the scene mistranslated between Jiang Xue Ning  and Xie Wei.