New Delhi, Jan. 3 -- During the two years he was held captive in Gaza, Segev Kalfon had a recurring dream: slowly walking through a supermarket, browsing each aisle for his favorite foods, taking in the brightly colored packages and smells.

Since being released on Oct. 13, his dreams have flipped: Most nights when he closes his eyes, he is back on a dirty piece of foam mattress in the 2-square-meter (22-square-foot) room in a Hamas tunnel where he was kept with five other hostages, counting each tile and crack in the cement to distract himself from severe hunger and near-daily physical torture.

"I was in the lowest place a person can be before death, the lowest. I had no control over anything, when to eat, when to shower, how much I wan...