tricky eyes

When I am at rest watching television or reading a book I will see movement out of the corner of my eye.  When I go to focus in the direction of the movement I see that nothing has changed.  Perhaps I will think someone has walked through the kitchen 25 feet away or that a bug has flown into view momentarily.  I do get severe motion sickness and have quite a few medical problems such as Hashimoto's Thyriod disease and Dysautonomia for which I take atenolol to regulate heart rate and am starting on Mestinon to help my swallowing and breathing.  I take florinef on and off to keep my blood pressure up and I'm not sure if these incidents happen more when my pressure is low but it would make good sense.  Please let me know what you think.
Thank you,
Foofie