so ive had a bad increase in cardiophobia 3.5 months ago and I had a check up and good ecg but ive still been worried.

I noticed that a night time my heart and body slows down. 

Now I started thinking. 

Is it the fact that my heart is physically more calmer that I feel better? like mostly my breathing and what not. Or is it because mentally im aware its not beating as hard and fast and thats whats preventing other worse symptoms to show up?

Normally I feel like I do some little exertion and my heart picks up and then I panic and my breathing gets fucked.

but at night those things usually dont happen. So now im wondering. is it because my heart is physically slower than i dont have all the other issues? or is it because mentally im calmer when my heart is calmer?