Varies: There is no specific dangerous heart rate during exercise. How fast your heart beats with exercise depends on a number of factors, especially your conditioning. If you are healthy, a heart reate in the 170's or even higher may be ok and tolerated.
Motion sickness caused by video games, sometimes called simulator sickness, is caused when there is a disconnect between what your eyes are seeing and what your body is feeling.
You get motion sickness when one part of your balance-sensing system (your inner ear, eyes, and sensory nerves) senses that your body is moving, but the other parts don't. For example, if you are in the cabin of a moving ship, your inner ear may sense the motion of waves, but your eyes don't see any movement.