Hello thanks for asking from HCM for your health related queries I can understand your concern. The symptoms like sudden onset palpitations, racing heart, shakiness and inability to stand still etc occurred most likely due to severe anxiety or more specifically due to panic attack. This can occur due to some underlying medical condition like Hyperthyroidism or Vitamin B12 deficiency, cardiac conditions or even anaemias. Please visit a doctor to rule out these conditions. Once medical conditions are ruled out then anxiety can be labelled as cause for your symptoms. Medicines like SSRIs as Fluoxetine, Paroxetine, Sertraline etc are used commonly in anxiety. For severe anxiety attack like you had medicines like low dose benzodiazepines as Clonazepam can help. These medicines help to reduce the palpitations and relax the individuals. Please visit your doctor for prescription. Thanks, I hope this helps you. Take care Dr. Seikhoo Bishnoi, Psychiatrist.