I actually thing there is something Realmatic going on. Remember how your spiritweb has to be a bit broken for a spren to bond with you? With an ordinary human with a broken spiritweb breaks, they have a Cognitive and Physical aspect as well, so one third of them is injured. When a Cognitive shadow has their spiritweb broken, one half of them is injured. So when their spiritweb broke, as it must have during Damnation, they were more affected by it than an ordinary human.