I am pleased to say the symptoms you have are physiological i.e. normal, and this is called an 'after image'. It is also linked to dark adaptation ,in which, when you come from bright or day light to dim light, as in a matinee show cinema hall, your eyes take 10-15 minutes to recover. On the same principle, airline pilots have special goggles when landing on brightly lit runways, before and after which, they are in almost total darkness when they are flying in the sky. I can give you several examples like this, which can cause visual hallucinations.