It was not a primary jungle -- I have seen such jungles in Borneo and Pará, Brazil -- it was a secondary jungle where the growth is very thick, but relatively low. It happened in Ko Samet (Samet Island) in Thailand a long time ago. It would take too long to explain why I got lost there, but anyway I spent one night in the jungle and noticed that the the night there is really dark: you couldn't even see your own hand if you moved it before your eyes.

(In the morning I climbed a hill, saw the sea and knew where I should walk.)

So making that movie would be quite cheap.