my cousin has exactly what you explained, i think its vertigo. when she looked behind her she goes very dizzy and feels sick. i think her's was caused because she used to be an air-hostess and apparently this can unbalance the wax in your ears = leading to vertigo. i could be totally wrong, but go to your doctors and tell him/her that you feel dizzy/sick when you look behind you, they'll know exactly what it is and then treat it
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