Do you have a rational reason to believe in what you feel and not dismiss it as a false belief? You can also look at it this way: so what if you're dead? That would just mean death is pretty much nothing and that what we know as life will continue uninterrupted after death occurs, because clearly that's exactly what has happened with you. Let's say hypothetically that you indeed died. Despite that, you're still clearly able to continue life as if nothing even happened, are you not? What, then, is the significance of death, and why does it warrant the attention you're giving it? It would be an entirely inconsequential event if it played out the way you believe. That would also imply that we're ultimately immortal because death would mean nothing more than essentially skipping deaths and living on in another reality/dimension, as evident from you still being here.
"like as a kid for example I was in a pool and almost drowned . what if I did drown ? what if I am already dead ?"
Rationally speaking, you didn't die because you're still alive. You did *almost* drown. There is a difference. You can arrive at the same conclusion by checking your vital signs. It seems to me like you're pondering if you died in an alternative dimension/alternative outcome or some such. Even if you would have, how does that have any relevance to you *here*? I also hit my head pretty badly as a kid and could've died, but I don't see that as grounds for believing that I died. Could have but did not!
You ARE alive. There is absolutely no reason whatsoever to believe otherwise. If you have the capacity to ask whether you're alive, you are. You're also able to keep on living just the same as before this supposed death, hence:
Scenario 1: You did not die, and your life continued normally. Good for you.
Scenario 2: You died, and your life continued normally. Good for you.
Conclusion: Death is inconsequential.
What really will happen is that you will die one day, and you won't be able to question whether you're dead or alive. Fine, it's worth acknowledging that some people believe in an afterlife-and I don't deny the possibility either-but why would this afterlife be identical, and seamless, to the life before it? That doesn't make much sense, either, does it?
In reality, this is nothing more than an obsession. Your belief is unfounded. I hope you can see that and hopefully shake it.
Regarding you asking if I've had this thought: yes, I've thought of something like this before. The difference is that it was just a normal thought going through my head, something I explored in a neutral and healthy manner as I love to explore abstract things. I also recognized it as an irrational belief. The takeaway here is that I didn't fixate on it as an obsession-and neither should you.