Dream, reality and the world inbetween DRAWI

Samantha, short Sam, went to her grandparents at age 4. There she disappeared for 2 weeks and came back with an old rusty knife. Since then she always has the same dream once her thoughts digress.
She’s chained in a cage in pure darkness. There is no other noise except the rattling of the chains when she moves.
Where is that? And why does she seem dead everytime she has that dream?