I think your point about possible cold water shock leading to cardiac arrest in the shower is way over the top
http://www.port.ac.uk/department-of-sport-and-exercise-science/staff/prof-mike-tipton.html
Professor Mike Tipton said:‘Cold water shock is one of the biggest stresses that you can place the body under. Cold water kills and it kills quickly.’
Read this article
http://magazine.rnli.org/Article/Cold-water-shock-A-bolt-from-the-blue-125
Bear in mind that Shirley Robertson was expecting to be immersed into cold water from ambient room temperature and was wearing a wet suit. Her skin temperature was reduced slower than had the water been applied directly to her skin. ""‘As soon as the water went down my neck I went into cold water shock instantly,’""
Cold shock in a shower involves a hot steamy atmosphere and hot water on the skin changing into cold water which is direct onto the naked skin and is un-expected.