I was sitting on my bed, talking, and all of a sudden, my heart started beating irregularly, too quickly, and hard. i could feel the contractions. are random palpitations normal? should i be worried?

Maybe : If this is isolated, in someone of your age it's most likely a benign condition due to some kind of stressor such as stress anxiety or even increase caffeine intake. Unless this is something that is common in your family or something that reoccurs often you probably do not need to worry. If you aren't anxious person or consume a lot of caffeine a good start would be to control those causes.

Very normal!: Palpitations are very common in the general population. Usually these consist of extra beats known as pvcs or pacs. These cause a chaotic fluttering sensation and take the breath momentarily away. They are most notable when stationary or lying down at night for example. Sometimes they may be evident at other times as well. Caffeine and stress potentate these common annoyers.