How to know if it's real?

[Claude]

Hello

Few years ago, I had a heart attack and during this event my heart stopped. I didn't realize what happened but when I opened my eyes as I woke up I was in the hospital. My last memory before hospital is being in my home bathroom.
I am afraid to die now, as I can die anytime soon and don't want to have nothing to experience.

I saw multiple posts here saying beliefs are just beliefs and everyone has different belief and different experience, they say different things and speculating but nobody sure that the experience was real. Can we be sure that death is end like it could be in my case? Can we be sure that death not the end?

How do you know that what you experience like seeing spirits, communicating with them, having glimpses of afterlife are real and not brain chemicals and reactions cocktail? Do you have proof, evidence? Can you be sure that experience is true?