Things I’ve found that affect motion sickness in me when using the mounts:
Visual Blur setting, was already low and increasing it did make the motion sickness worse.
The amount the camera would ‘jump’ with the mount. Zooming out to the point where the camera would no longer move up and down when the mount jumped helped.
The difference between how much the character bobbed around when on a mount vs when no mounted. I found that playing on a min height female Asura caused the motion sickness to go away vs playing on an short but not min height female human which causes motion sickness. I think the reason is I’m so used to seeing Asura bob around due to their more expressive animations that the mount bobbing feels more natural on them (making it feel normal to me) vs jumping back and forth between the more static human character and the mount.
How much I actually looked at the character when playing. When I play Asura I tend to not look at my character as much due to their smaller size and instead use the action camera cursor as the ‘reference point’ for where the center of the screen is. On humans the actual character becomes the ‘reference point’ due to them taking up more screen space in the center. Paying less attention to my character when playing a human did reduce the amount of motion sickness.
One other note is that my first time using the mount the motion sickness was far worse than it is now but I still feel it some when playing certain characters.
Things that in general cause motion sickness in me:
camera shake (which I have off in Gw2 and thank you for making that an option)
games drastically moving the camera without my input or making the camera ‘sticky’ so it doesn’t instantly move when I tell it to.
control schemes in 3D games that I’m not used to yet (and goes away after getting used to it)