Hi. Everybody's pulse rate increases when they do physical activity like walking and climbing stairs. If you feel uncomfortable sensation of heart beating with minimal activity probably your exercise conditioning is low and since your not used to much physical activity the increase is very fast and very exaggerated. You could do some form of regular aerobic exercise to increase your exercise conditioning and vagal tone which brings down the resting heart rate and increases your reserve for physical activity (in short increases stamina) Having said this if your palpitaions is very disturbing and more on getting up from lying position you could have something called POTS. In which pulse rate increases disproportionately on standing from lying. It's not a life threatening condition andcan be managed easily with postural exercise and rarely minimal medication.

Any difficulty in breathing? Echo? Thyroid status