Patient Presents Involuntary Rapid Side To Side Eye Movement Usually

patient presents involuntary rapid side to side eye movement usually in bright light and has had a sudden problem with balance when standing or trying to walk. Patient has recently undergone surgery to remove left kidney and ureter on Dec. 22 2016 . Cancer was present in the ureter. Operation was successful. Was to begin with radiation and chemo treatments when these two symptoms presented. CAT scan was done and nothing seen--i.e. tumors or bleeds .MRI next. No seeming loss of strength on either right or left side of body. Any thoughts on the situation? Thanking you in advance. J Jansen