Increased heart rate is called tachycardia.
There are many causes of Tachycardia(fast heart rate)-
It can be due to sinus or non sinus origin.
Non sinus tachycardia are either supraventricular or ventricular.. Ventricular tachycardias are more serious in nature
Sinus tachycardia is defined as a heart rate of greater equal to 100 beats per minute originating from the sinus node
It can be due to anxiety, panic attacks, dehydration, deconditioning, volume loss due to bleeding or other loss of body fluids, hyperthyroidism, electrolyte abnormalities and many other conditions.
My advice is that you need EkG to view status of heart, and find the cause.
You should consult your Physician soon .