Anticholinergics such as diphenhydramine (benadryl) and dipehhydrinate (drammamine) can cause visual disturbances (such as wavering lines, moving shadows, mists, etc) and even full-on hallucinations in higher dosages. Many people are sensitive to these chemicals (and circumstances can arise that make anyone temporarily sensitive) and can experience visual disturbances even in the recommended dosage range. Furthermore, many people take multiple "cough and cold" remedies at once not realizing that they are doubling up on some of these chemicals.

Just a thought.