This is not unheard of -
SpringerLink - Journal Article
morophine can also cause this -
Morphine Side Effects | Drugs.com
I would suggest talking to a medical doctor immediately and going to the ER if these hallucinations are currently happening.
If you're just looking for some general information on this I can probably do some research into this topic for you at a later time. My best friend is an MD, but I'm on vacation with him and we're at a NASCAR race right now so I don't think he'll have time do look into this any time soon. I also don't have access to my university's scifinder here so I can't read the data in that article for you, but if you or someone else has access to scifinder they can easily get the full paper.
Honestly though if someone is experiencing hallucinations I would suggest going to the doctor or at least phoning the ER and asking if you should come in (phoning them is at least free).
hopefully you find the articles useful. Good luck.