I had these throughout peri & for a few years postmeno before starting HRT, in long episodes at any time of day 24/7, but worse in evening & overnight. They resolved shortly after starting HRT 3 yrs postmeno, with a change of thyroid meds around the same time.
Agree they are v scary & can be overwhelming, but they are also fairly common in menopause, though I didn't know that until I saw a v good MS 3 yrs postmeno. They started nearly 20 yrs ago & back then there was much less awareness about the effects of menopause so the various medics I'd seen prior to this MS were not sure of the cause, which compounded the worry, especially as I also have a thyroid condition. Like some of you, I had all the cardiac tests & only benign ectopics were found.
Now 12 yrs postmeno I still get them occasionally, usually in response to a change of HRT or thyroid meds (dose up or down) but they tend only to last for a couple of weeks & are minimal compared to peri. I found Utrogestan brought them back with a vengeance though & couldn't take it due to this & other horrible side effects.
Controlled breathing, regular meditation & anything that promotes relaxation can help bring about a calmer default state & reduce the emotional havoc they can wreak. There are many, many threads on here discussing ectopics if it might help to search & see that you are not alone & find out how others have managed.
Wx