I don't know, i'm no expert, and certainly not a judge of what is normal and what is not. I do know that 'normal' isn't the same for everybody.

But if you get a serious event in life (example, death of family member or other loved one), that makes you doubt if you still enjoy life or whats the use of 'finishing' it till your body gives up.. those thoughts will occur, sometimes swiftly sometimes occupying your brain for longer. Do keep in mind, having thoughts and actually acting upon those thoughts are two different things.

Though pondering if tom sawyer has brass handles on his coffin.... Maybe if i was reading tom sawyer, yes that would probably be a thought that came before others. :) Have to admit, i never read that book, so not entirely sure why one would fantasise about his funeral.

Tom Sawyer is sitting in the rafters watching his own funeral. There's more than one sequel, and he survives all of them.