I Am (25 Year Old) Having Frequent Heart Palpitations Which

I am (25 year old) having frequent heart palpitations which feel like the heart beat is stop for a second and start with hard beat. In day time I am not able to feel any symptoms. But during night time when I am drifting to sleep if palpitations occurs I feel like I am fainting ,blood rushes in brain, stop breath for a second and making me to wake up. because of that I become scary to sleep. What is the issue with my heart? I took ECG, Echo, TMT and electrolyte blood test which comes normal.