deb,

Thanks for your question.  Though the dizziness and insomnia are possible side effects, the dizziness would not be positional in nature.

Much of what you're experiencing could be from an inner ear (or vestibular) problem.  These symptoms are brought on by changes in position, as you have described, and can take weeks to improve.  Another thought is a problem with your carotid artery, especially because you sometimes get these symptoms when you are backing out in your car. 

Your doctor's suggestion of the motion sickness medication is quite reasonable.  However, if there is no improvement in a couple of weeks, then a re-evaluation of your symptoms by your doctor is indicated.  Your might require some testing to check out the carotid artery, and/or inner ear area.  These tests might include an Xray or scan.  Please discuss these possibilities with your doctor.

If the effexor is the cause, your symptoms should clear over a couple of months.

Best wishes.

Martin Cane, M.D.