Hello, 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 can have 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. So visit nearby cardiologist for these investigation. Also, hemoglobin and thyroid test should be done. Is there any stress or anxiety associated, as it can lead to palpitations. Also, Rather than stopping, metoprolol dose can be decreased to 25 mg or better option, you can ask to decrease the dose of lisinopril. Stopping metoprolol can cause increase in palpitations. The decision will be taken after seeing the ecg, as what the cause of palpitations and all. If bp goes down, you can have salt and sugar water whenever needed basis.