Extrasystoles for several years, psychological or physical?

The following issue has been bothering me for about two years now: During a very stressful time in which I was under a lot of pressure (I'm in my mid-20s), I suddenly started feeling my heart flutter. I measured it, and it turns out that it's causing extra heartbeats, or even a single beat, several times within a minute.
During this stressful time, this continued for quite a while. I went to the doctor, but he just said I was crazy and didn't take me seriously—thanks for that. Another doctor suspected a panic attack. So far, that sounds logical. The psyche can certainly trigger a lot of things, so the keyword is psychosomatics.
This stress lasted quite a while (professional, looming unemployment, etc.) until a solution was in sight, and things have been looking up since the beginning of this year. My life is currently so perfect that it couldn't be better.
Unfortunately, I keep waking up in the middle of the night with a fright (bad dream, etc.) and feeling my heart almost pounding out of my chest. And sometimes my heart even suddenly skips a beat. It's not the usual fluttering that I feel, but rather a truly depressing, slow pulse that simply stops for a moment.

Before I run back to the doctor, I'd like to ask here if anyone has ever experienced something like this. Is it simply psychological and does it take time? I know how unlikely cardiovascular disease is in your mid-20s, but it's not impossible. I have to mention: – high cholesterol (inherited) – reflux – I smoke (vape).

I would be happy to receive an answer.
Oh yeah, they did three ECGs. A stress test and a long-term ECG at the cardiologist were unremarkable (although I didn't have any problems during those times; it was always in phases). An ECG at my family doctor clearly showed the extrasystoles. My Apple Watch was also able to record them repeatedly.