I understand the feeling. I felt it often as a child and would run to my parents crying about it in the middle of the night. It's the dread of utter dark—like every light in the world going out at once.

It turns out this question—how do we contend with the question of death?—is one of the most, if not the most, studied questions in human history, second perhaps only to why we came to exist. The collective answer by each of the world's cultures is encoded in myth, poetry, and spiritual and religious traditions. I would recommend the Bhagavad Gita, translated and commentated by Eknath Easwaran (https://www.amazon.com/Bhagavad-Gita-2nd-Eknath-Easwaran/dp/...). It's not necessary to practice or believe in any particular religion to gain something valuable from these books, nor is it incompatible with science to delve spiritually.