I'm 21 finished eating, was sitting and my heart started beating really fasthappened once before when I got up from bed. Felt sluggish today and tired?

SVT. You're describing symptoms of a tachycardia - in your age group, probably svt but can be other things. You need a cardiac evaluation to rule out serious conditions. That said, the majority of 21 year olds will be found to have a healthy heart with "abnormal wiring" which was present since birth. Depending on frequency, it can be treated with meds or ablated with radio-frequency.
21 yr old fast heart. You have had two episodes of palpitation and you felt your heart beating real fast.You should see your doctor you may be getting sinus tachicardia or atrial oe supraventricular.You need to be checked for hyperactive thyroid, and nedd a resting ekg.I hope you are not drinking too much coffe or one of the energy drionk which is loaded with caffeine, or any other drug as that can cause fast heart beat.