A portal is not a road for Geralt
Geralt’s mutations make him extraordinarily capable in a fight, but they do not make him immune to every kind of discomfort. Portal travel is a different problem from facing a monster: it abruptly carries him from one place to another, without the ordinary cues of a journey—movement, changing scenery, or a gradual sense of direction.
The games treat that magical shortcut as something his body still reacts to. The nausea is a character detail, not evidence that portals physically injure him or that witchers are generally fragile. His enhanced abilities have limits, and this one is an especially ordinary one.
A small weakness with a useful effect
Geralt’s profession can make him seem almost purpose-built for danger. Showing him suffer from portal travel punctures that image without diminishing his skill: he can endure a fight with a vampire and still feel awful after an abrupt magical trip. The contrast makes the fantasy’s powerful magic feel less like effortless convenience—and makes the monster hunter feel more like a person.
