Talk to Internal Medicine on Pain And Numbness In Left Arm

My mother has been experiencing a fast heartbeat along with numbness in her left arm, where she couldn't feel anything. An ECG was conducted, which showed a heart rate of 120 bpm. We consulted a cardiologist, who prescribed blood-thinning medications and suggested further tests. All the tests came back completely normal. However, her blood pressure spikes when she feels stressed. The doctor at Ittefaq Hospital diagnosed it as stress and prescribed medications for stress and blood pressure, which have significantly improved the condition of her arm. Despite this, we still want to understand the root cause of the problem. Since all heart-related tests are normal, and she does not have diabetes, what could be the actual reason for these symptoms?