Hi! my heartrate goes up to 135 when climbing stairs and then drops down to 55 (slow for me) when i sit down or lay down within 2 mins. is it normal?

Tachycardia: Unless you're running up the stairs, that is a rather fast heart rate after stair climbing.Do you note rapid heart rates after other activities? Do you get short of breath also? I feel that you should have a heart and lung examination and also be checked for anemia and even an overactive thyroid although your heart rate at rest is not elevated which may rule out hyperthyroidism.