Hello, There can be many underlying causes which can lead to weakness, fatigue and increase in pulse rate too. It can also be due to anxiety, stress or other reasons. Age too is an important factor which needs to be considered. We would suggest not to get anxious. It is better to consult a physician and if needed a cardiologist since you have a family history of related to cardiac issues. The doctors will surely guide you. Hope our answer helps you. Start out with a physician, they would provide further references based on tests & examinations - General Physicians in Mumbai.