What Causes Hallucinations After Taking Propranolol?

I was prescribed propranolol for migraines I started having hallucinations at night. I see people in my bedroom trying to kill me or my husband. They are so real the next day I can describe the cloths they are wearing down to the buttons on there shirts. I have these hallucinations 6 out of 7 nights week. My doctor is taking me off of them for 4 days to see what happens.. This has been going on for almost 6 weeks. Your thoughts