Terrible! Every doctor you see...make sure that drug is recorded on their records as you having an allergy to it. Don't know if that is considered an allergic reaction, but it doesn't matter. DH was given a medication once that was causing him to fall down. It confused him on spatial orientation where he thought up & down was sideways, etc. Scary! I figured it out what was causing that, since the doctors were obviously not going to. As soon as he stopped taking it, the symptoms went away.
