Spren in general have wildly different forms in the cognitive realm than in the physical. Passing between also causes them to lose sentience in most cases.

Humans, on the other hand, are physically and mentally unchanged by traveling between.

Is there a particular reason for this? It could be that Spren are investiture based while Humans are matter-based, but there are issues with this. The spren seem to have very physical bodies built of actual matter in the Cognitive realm. A certain scene in RoW implies that a more direct transfer is possible, in principle, but spren can not survive it. The asymmetry is particularly glaring in this case, as any physics-physiology issues should work both ways ie a human drowns in water, while a fish suffocates on land. A spren who is artificially blocked from changing forms... [mumblemumblemumble]s when coming into the Physical, while a human the other direction is unchanged by default and just fine with it.

This may just be narrative convinience that I am overthinking, or that a cognitive-human anti-spren forced-transfomration would be borderline body-horror, (though I am morbidly curious what a sprenified human would look like) but I can not help but think this is a setup for something. Thoughts?