abyss

"Her sadness was so deep it felt like an endless abyss"

"Don't step too close to the edge, or you might fall into the abyss"

"Do you ever feel like you're staring into an abyss when you look at the night sky?"

"The deep hole in the ground looked like a dark abyss"

"After losing his job, he felt an emotional abyss of despair"