What Causes Dizziness And Eye Floaters Post A Bout Of Flu?

Its my elderly mum 84 years old has not been well for the last month or so had flu symptoms and only now recovering slowly. She now experiences disturbing episodes whereby out of the blue she sees flashing lights to her left hand side moving up and down - coming and going. Lasts for a few minutes. Today, she lay down for a nap and the ceiling started moving around. She is getting quite nervy and jumpy about this and it is very unsettling for her can you help