Normally the heart rate of an adult human is 80 Beats/Minute in restful condition. It rises proportionately with physical exercise, dehydration, temperature, nervousness, anxiety, sympathetic stimulation etc.. As you said, you are working hard with not enough intake of water for the last one day, most likely you have become dehydrated next day and your body normal physiological mechanism came in to action to maintain homoeostasis by raising your heart rate. Anaemia & Anxiety can also lead to rise in heart rate, but the last two condition have a history of longer duration, not of two days only, as your case is. What you can do is --- [1] Take rest [2] Ensure proper water intake [3] Monitor your blood pressure [4] Don t Panic If the condition does not normalises after 1 or 2 days, take the help of nearby physician. Thank You (Viewer rating for my reply is expected).....