Thank you for your query. Would you please clarify a few things for me? 1) Is your mother hypertensive/diabetic? If so, what medications is she on? 2)does she have any history of heart disease? Thyroid disease? 3)has she been ill recently? 4)how old is she? 5)does she have these symptoms when she lies down or whenever she changes position? 6)has her level of physical activity changed significantly in the past couple of months? 7) does she have any breathing difficulty? 8)the spasms the her legs, are they painful? Do they go away on their own? Does she pain when you squeeze her calves or are they red /inflamed? 9)any family history of the above? Any alteration in the heart s rate and rhythm should be immediately investigated, especially when she has dizziness and fatigue. The answer to the above questions will allow me to help you better. The heart is responsible for keeping all the organs in your body supplied with oxygenated blood so that they make use the energy to carry out their functions. If it s too fast (hence ineffective), circulation can get compromised and symptoms like giddiness appear. If she has any of the illnesses. I mentioned above and she is mostly sedentary, she may develop clots in the blood vessels (due to stasis) that can dislodge and travel through the circulation and result in compromised blood flow to certain organs/tissues Certain inner ear disturbances may also cause giddiness and fast heart rate I recommend that you take her to the ER. She may require a cardiac workup(electrocardiogram and an echocardiogram,) x-ray, blood work Take all her previous medical history details along (if any). Do not leave early her alone unless she has been looked at by a doctor and it s safe to do so. Hope this helps. Please get back to us for any further questions. Wish you both good health