Why am I hallucinating?

It could be anything from a migrane, to a seizure, to neurological problems, to a tumor, to mental illness to an allergy or reaction to non-narcotic medicine or chemicals. Let your doctor know what's up. There are too many variables for you to figure it out on your own. It could be someting big or it could be somethning small. You need more information. Let the professionals handle it and try not to worry until you know what to worry about. I know that's easier said than done!