I always wondered that in these reincarnation mangas if they actually died in their origin...

I always wondered that in these reincarnation mangas if they actually died in their original life or if another soul from a different world got stuck in the main characters original body. And also if the person from the body who the main character wakes up in is truly gone or just got sent to another body. All I can imagine now is that scene from the Scooby-Doo movie where their souls were jumping from each other bodies