I took mefloquine in the 1991 for about six weeks while travelling in South America.  I had crazy dreams of being chased which left me feeling paranoid and uneasy during the day.  By about Week 4, I started to have hallucinations of tarantulas while awake.  I would turn my head while sitting at a table, and there would be a spider sitting on the floor or on the curtains.  It was very vivid...I can still picture them and the detail which they had.  It happened maybe four times a week for a couple of months, and then tapered off, but I still saw the occasional spider for about a year.  I told my doctor upon my return, and at that point she hadn't heard of any mental side effects beyond depression.  It wasn't until years later that I realized I wasn't crazy to believe that those dreams and 'spiders' were an actual reaction to the drug.