Sinus tachycardia otherwise normal ECG.

Since last few days i have felt that with change in posture my heart rate changes. When i stand its highest 105-116 bpm When i sit its 90-100 bpm When i sleep its 75-85 bpm However the BP more or less remains the same So i decided to get ECG done While doing ECG the report was as follows: AGE: 22 years Pulse: 123bpm Conclusion: sinus tachycardia otherwise normal ECG Problem that i am curently is nothing but only sense that when i stand i could feel palpitation in my neck and chest. Do not have any other symptoms. But i want to point out one thing that while running on treadmill at 5,6,7,8km/hr i did not feel any discomfort as well as my pulse was between 100-120bpm but as soon as i stopped the activity the pulse raised upto 163 bpm and then started declining. Also at that time my bp was 140 and 75. Can you tell me that whether there is something to worry ?