Hello, There are multiple possibilities like heart issues or even anxiety related. This can be a cardiac arrhythmia like psvt or atrial fibrillation, in which heart rate suddenly goes up and also suddenly decreases. Blood pressure falls during these episodes and one has dizziness, fainting, blackouts, sometimes syncope. Usually ecg is normal as it is usually done in between the episodes. ECG done during episodes will show abnormality. You will need 24 hour holter monitoring if symptoms are occurring in daily basis. So visit nearby cardiologist for these investigation. Also, hemoglobin and thyroid test should be done. ln order to abort such episodes you should try to cough hard. Is there any stress or anxiety associated. Till the time your evaluation is complete, you can ask your local doctor for tab ciplar LA 20 mg once a day. If none of the above is successful then last option is of electrophysiological studies which is invasive test which can diagnose and treat the arrhythmia permanently in most of the cases.