If you are afraid of being buried alive, you can always choose to be embalmed. If you aren't dead at the beginning of the process, you certainly are by the end!
But, to be serious, I have seen several dead people - my mum and dad, my little baby niece, and quite a few of my in-laws as they are Hindus and always have an open coffin. None of them looked like they were still alive.
One of the biggest surprises, though I tried not to show it, was when my brother-in-law's ex-wife died in the night from a heart attack and we went round straight away in the morning to comfort her sons. When we got to the house, one of her boys said "Do you want to come upstairs?" and I said yes, because I thought that her youngest son who lived with her was up there. Instead I was led into her bedroom where she was lying in bed. It was a bit of a shock, as she did look extremely dead, but I tried to look as if I had been expecting it. Later, people said that she looked like she was sleeping. No, she didn't, not a bit.
I mentioned this later when I was chatting to my GP. He said that he had seen hundreds of dead people and none of them looked like they were sleeping. They definitely looked as if some vital essence had gone.
Where, how and if that "essence" still exists is a matter of belief. I comfort myself with the thought that maybe we do go back into timeless energy - "like a drop of rain flowing to the ocean" as we Pagans believe/hope - but, if I'm wrong, I won't know and therefore it won't matter.
As Mark Twain said, all the millenia when he didn't exist, before his birth, caused him no inconvenience at all, so why should the millenia after his death bother him?