Why is shmuel particularly unhappy when he shows up at the fence after being absent for two days?

Shmuel is particularly unhappy when he shows up at the fence after being absent for two days because he feels that his situation has worsened in his absence, likely due to the harsh conditions he endures in the concentration camp. He is also concerned about the well-being of his family and friends, fearing for their safety and suffering. His sadness reflects the grim reality of his life, as he realizes the impact of the ongoing atrocities around him.