P2319H, dizziness using portrait mode

I recently bought a Dell 23 Monitor - P2319H. I loved the idea of using a second monitor in portrait mode. However, the first time I used it, it gave me a massive dizzy spell, after just 5-10 minutes of use. It was fine until I switched my gaze back to my laptop (which is obviously in landscape mode).

Has anyone else experienced this, and does the dizziness go away over time? I can't afford to the 15-20 minutes it just took me to recover.

Thanks