I would say look into near death experiences. Now i understand most think that these experiences are just DMT trips the brain takes, which is why I recommend looking into the case of Dr. Eben Alexander, specifically, a neuro surgeon that had a highly documented near death experience. He had a near death experience while his brain was non functioning and non responsive, monitored by his fellow neurosurgeons, his brain wasn’t functioning to release the DMT, and shouldn’t have been able to retain any memory at all, and yet had a near death experience that he remembered during the time of documented brain death.

http://ebenalexander.com/books/living-in-a-mindful-universe-a-neurosurgeons-journey-into-the-heart-of-consciousness/

Also, there are quite a few videos on YouTube interviewing him.