Medical question Tachycardia.?

I started taking Avelox and Allegra D for a sinus infection and bronchitis on Thursday. Friday afternoon i was in the er due to rapid heart beat it hit 163 at one point they said i was severely dehydrated and the decongestant probably caused this they gave me 3.5liters of fluids and a steroid shot and said a had a episode of Tachycardia and i should be fine well i have been monitoring my heart rate it is never under 100 its usually 120 bpm in the morning and 100-120 bpm through out the day I haven't taken anymore of the avelox or Allegra since thursday at 12:30 pm so I am wondering why is my heart rate still so high i have been resting and taking it easy I have a good monitor so i know it is accurate my bpm usually was in the 80 bpm before this all started