What causes tachycardia/pounding heart wheb laying down? not anxiety

See a doctor: arrhythmia,which mean abnormal heart beat,could be simple tachycardia easy treat it with medication. or it could be complicated and with consequences, like atrial fibrillation could cause a clots to the vital organs in the body like brain with stroke or kidney or guts. or it could be a bad tachycardia that could lead to fibrillation and cardiac arrest. so please see a doctor

Tachycardia: There might be a number of reasons, do you have overweight problem ? Do you feel extra - skipped beats. Your doc should be able to tell why you have these symptoms after examining you.