2 possible reasons…
First You may be getting motion sickness or in this case simulator sickness This is caused by a disagreement in your brain between what your eyes see and what your inner ear reports.
Remember the inner ear is responsible for balance. So the easy flow of the scroll is tricking your balance center into thinking that you are moving when you are not.
One theory about motion/simulator sickness posits that it occurs because the area postrema portion of the brain associates the visual/balance discrepancy with hallucination.
Your body associates seeing things that are not real with poison in the body and it wants to purge that. So you feel sick.
One way to help is to try sitting farther away from the screen so that it doesn't fill your field of vision. Also, experience often helps you get over it.
You essentially condition your sensory centers to accept the visual input as "not harmful"
white paper on simulator sickness
http://www.hitl.washington.edu/publications/r-96-3/
Second possibility…
You can also get the same feeling using an iphone or any wireless device.
There is some studies out that show that a percentage of individuals in the world are sensitive to either cell phones or wireless devices and in some cases wired devices.
The current culprit seems to be EMF (Electro Magnetic Frequency) sensitivity.
EMF's are energy waves with frequencies below 300 hertz or cycles per second. The electromagnetic fields we encounter daily come from every day things such as power lines, radar and microwave towers, television and computer screens, motors, fluorescent lights, microwave ovens, cell phones, electric blankets, house wiring and hundreds of other common electrical devices.
Some individuals show a higher sensitivity to these waves and can complain of headaches, dizziness nausea etc. While other people are not effected at all.
The World Health organization has a page that discusses the theories and studies around this phenomenon
http://www.who.int/peh-emf/about/WhatisEMF/en/index1.html
I have problems with cell phones and inner ear vestibular dizziness for awhile. Thank goodness for iphones included earbud/microphone which cuts down on this dramatically.