My friend was having some acute mast cell activation, probably due to a parasitic infection.  She was taking several different antihistamines and at one point began hallucinating.  The pruritis was so bad that apparently she had a little too much antihistamine which caused some crazy symptoms, including hearing a choir singing, seeing animated teddy bears in the tree outside, and others that were pretty frightening, X-Files kind of visions!

  The point here is that doctors can tell patients what they believe is the maximum dose of an antihistamine, but it might just be simply too much for that particular person.  If you need to add something for breakthrough symptoms, make sure someone else is around if possible.  

  Only add one medicine at a time, and write down any changes in your feelings or behavior.  Try to alternate meds so you aren't taking the same thing all day every day.

  Be sure to read about any and all meds you are taking or plan to try.  Read especially well the interactions with other meds and/or foods and the signs and symptoms of overdose.

  Luckily, the outcome in this case was to cut out some meds, and the hallucinations went away!

Not as scary as it was for her husband!