HI, thanks for using healthcare magic Congrats on smoking cessation. The smoking cessation significantly reduces the risk of heart disease, stroke, cancer. Cessation is not normally associated with weakness and increased heart rate. There is likely another cause that needs to be explored via physical examination and blood tests. Blood tests would include a full blood count to rule out anemia and thyroid disease to check for low levels. May also need heart evaluation as well- ECG, echo I hope this helps