I'm woken in the night by my heart racing so fast. what could this be. i have low blood pressure and have just started taken toprimate.

Several things maybe: It could be anything from anxiety to nightmares to the thrill of having watched Peter Pan live on NBC the other night and realizing that two of the actors in the production were from Cleveland, Ohio (where I live). Or, it certainly could be a side effect of the topiramate if you have only been taking that medication for a few days or a few weeks and this started right after it.