First of all, your response is pretty typical. Many people who experience heart rhythm issues tend to become very afraid they will drop dead. It is a logical reaction to our heart acting up because we do need our hearts to survive so our survival instincts kick in. It is important that we talk ourselves off the ledge so it doesn't take over our life or we can fall into obsessing about it, which really doesn't solve anything and just makes us miserable. I know easier said than done, but it would really do you an extensive amount of good to tackle the anxiety. Not just for your heart issues but for your everyday life. Maybe do some research, find books or even see a counselor for a few visits to gain some tools you can use to counter the anxiety when it gets triggered.
With that said, there is no way to tell for sure that you are having vtach. Considering you have had a few echos that showed your heart was healthy, odds are it isn't Vtach or something related to heart disease. It very well could be just a run of isolated pvcs (more on that later) or more likely a run of pacs. That said, at worst, it could be an undiagnosed svt like avnrt. Avnrt episodes tend to aggravate premature beats, pacs in the atria and pvcs in the ventricles. And premature beats often precede an svt episode. Without going into the mechanics of it, it's caused by being born with extra muscle fibers in the heart that can lead to an episode of rapid heart beat caused by the heart signal getting caught in a loop pattern, in cases of avnrt, it would be around the avnode.
I had avnrt and it felt like my heart was suddenly beating chaotically fast and it would stop just as fast, in one beat. It is the tell tale sign of an svt so if you feel that it could be that as opposed to vtach which tends to feel less chaotic and more like rapid thumping. At least the one episode I had was like that. With avnrt, I felt light headed and it was hard to breath. I had rare episodes when I was younger but they became more frequent as I got older. They always stopped on their own but coughing, holding your breath and/or drinking a cold glass of water or splashing some on your face can help break the episode up.
The only cure for svt is a cardiac ablation but they consider the condition benign. It really only may become an issue as you get into your 60s and/or if the episodes don't stop. Since you are able to stop them on your own there is very little wear and tear on the heart so you should be fine. But the only way you can be diagnosed is with a heart monitor. In cases of svt it is best to get a 30 day monitor. The 24/48 hour holters just don't offer enough time for a person with svt or vtach to have an episode for it to be captured. They are great for catching daily premature beats but not the less frequent rapid heart beat episodes. I had a holter and had an episode the day after so I needed the 30 day monitor to catch mine. Either way, it would be helpful if what you are experiencing happens at least every thirty days. So if you go to get a monitor try and see if you can push for a 30 day.
Everything considered, with your heart being healthy and whatever is going on not sustaining, you are at very little risk of sudden cardiac death. That generally happens after there has been some sort of damage to the heart after a heart attack or from a leaking valve causing scar tissue. Or from undiagnosed cardiomyopathy but you don't have that or your echo would have shown it. So, if by some chance, you are having a run of pvcs, it may still not be considered vtach if they are isolated. Meaning they aren't being caused by the heart signal being caught in a loop down within the ventricles. We can have a succession of pvcs in a row and it is called vtach but if the signal isn't caught in a loop odds are the heart will correct itself on its own. Of course I am not a doctor and can't say that with absolute certainty but that is what my research revealed to me. In an otherwise healthy heart, which you have, pacs and pvcs or runs of them are not a threat. Of course if what you are feeling starts to sustain for extended periods of time, it's best to get the monitor and get it diagnosed.
I will admit that I let an episode of avnrt go on for 8 hours and it wasn't the best idea. I figured I would take a nap and wake up with it gone but I was still in the episode. I did wear out my heart a bit and was pretty physically tired after that for a few days but it didn't adversely affect my heart. In my 60s it may have but in my 30s with a healthy heart, our heart is pretty resilient. I tell you this to point out that our hearts are very strong muscles that can handle a lot and still keep ticking. If we have healthy hearts we have very little to worry about in regards to dropping dead. So we need to be responsible about our heart issues and not completely ignore them but if we have been checked out to have a structurally normal heart we can probably safely say we will be fine. I know this is all very scary but just try to remind yourself that you will be OK, that you are OK. Work on getting on top of your anxiety and maybe see if you can get a 30 day monitor to catch what is going on so you know for sure. It's probably not vtach but know that for sure may help ease your mind. Take care and let me know if you have any other questions.