Hello everyone I'm 18 years old and whenever I lie down to my bed, or get up and stand still, I feel my heart beating hard, but not specifically fast.

When I lie down I can hear my heart beating and its really annoying that makes me feel uncomfortable. I was born with a biscupid heart valve, but I get checked yearly and they haven't found a problem yet.

I also had a checkup 2 weeks ago with my cardiologist who told me my heart is fine(he did an ekg and echo), but I have some arrythmias(both brachycardia and tachycardia) . I also have chest pains which are sharp and last for a few seconds.
My blood pressure usually varies from 13/7 to 11.5/6.5 it usually is around 12/7 at rest

Every doctor I've asked about my chest pain, blames anxiety. I also have had my thyroid checked and had some full blood tests which were all were clear.

These chest pains and the heart beating hard but not fast are driving me crazy. Could the arrythmias cause this? everytime I lie down and try to sleep I think I might die or something. But every other time of the day, like when I'm walking, sitting on a chair studying etc I don't feel these discomfort I'm also going to get a 48hour Holter monitor In a week or so. But I really feel I had have to ask.

No other health conditions. I'm pretty health and have a Good diet, I don't smoke nor drink. Nor previous incidents of heart disease in my family...