What dose it means when your pulse is running high and your sitting down?

Caffeine. If you are resting and your heart rate is still fast it could be from caffeine among other things. The heart compensates by increasing the heart rate when people have heart failure but just checking when you are sitting down isn't enough information. If you are constantly tired, need to rest during the day then see your doctor.
Pulse. Your heart rate varies at times. It could mean nothing or such things as a cardiac problem, anxiety, or others.