I know this is too late in internet time but since I'm replaying ARR, Kan-E-Senna does explain (in the Mih Khetto's scene if you started in Gridania) that the side-effects of an Echo vision can sometimes be confused for aether sickness. Explaining how the merchant at the start thought you might have it, even if your character is (head-canonly) Eorzean or you mention it not being your first time in Gridania.