23 male, 5ft 11, 140 lbs

In june I had 2 big stressful events which caused me to hyper focus on my heart. I had an ecg and general vitals check up done and it seemed fine. 

My main issues were feeling that my heart was too reactive and my breathing was all bad.

Over the past couple of days my heart slowed down and my breathing seems better but idk if thats a good thing or not. 

Im feeling a lot more fatigued and tired. My body feels like it normally does before bed but its like all day.

My normal sitting rates were 70-80 and my standing were 90-110, now my sitting rate is 60s and standing is like mid 70s.

It feels like my body is out of adrenaline or something. Its like my bodies depleted of energy. idk if this is like normal anxiety fatigue or if my hearts actually going worse?

I feel calmer physically but mentally im still worried. Where as before I was worried it was too fast to reactive now I worry its too slow and un reactive. 

I feel colder, slower, weaker, more tired, and a bit dizzier. Before I always felt a bit wired and too warm.

Another important thing is I've felt this way before so so so many times but I just wasn't obsessed with my heart at the time. I remember very vividly where I had these "sleepy days" before my heart fears got bad. I just assumed I was tired or depressed and they went away. I just never focused on my heart like I do now. I assume this is normal but im just worried again.

The temperature in the house also made a huge drop since it got so cold suddenly. Before the house temp was always around 78-80 but now its like 73-76.

Could it be that the summer caused my heart to be a little faster and then I reacted badly and now that its colder everything's lower and im more calm? Or could it be general anxiety fatigue? OR could it actually be my heart really failing?

Im also in the process of shifting my bedtime from like 3:30-4 am to 2:30 am. Could this be a reason?