Thanks for your question on Health Care Magic.
I can understand your concern.
Since your symptoms are only when you are not doing anything, possibility of
stress related symptoms is more.
But better to rule out heart diseases like
arrhythmia (rhythm disturbances in heart) first. Because arrhythmia can cause similar quivering feeling in heart.
So get done ecg, 2d echo and Holter monitoring (24 hour continuous monitoring of ecg).
If all these are normal then no need to worry for heart diseases.
Avoid stress and tension, be relax and calm.
Divert your mind from this feeling.
Don't worry, you will be alright.
Hope I have solved your query. I will be happy to help you further. Wish you good health. Thanks.