1. Motion stimuli is just anything that is perceived as a lot of motion to your senses. So walking around in crowded stores, driving in the rain, walking fast etc. Does your dizziness get worse when you look up, down or to the sides? Welcome to my world LOL :) I promise it won't kill you, I had a low level of dizziness for as long as three months once, mine is caused by estuation dysfunction.
2. Cymbalta is a good drug but a powerful one and it can cause varying side effects. The first time I took it I had started on a different drug first and ramped right into the Cymbalta and had no issues except for a day or so of stomach upset. The 2nd time I tried it I had a weird panic attack in the middle of the night and promptly stopped using it. If you can hang through the side effects when starting out Cymbalta is a very effective drug that really helped me get past a serious episode of GAD.
Hang in there.