Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. This can be a cardiac arrhythmia like 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. Did you have symptoms during your holter monitoring, if not then it may be missed, and in that case longer monitor like loop or event recorder or mobile based Alivecor monitor may be used. Also, hemoglobin and thyroid test should be done. In 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. Hope I have answered your query. Let me know if I can assist you further.