How so? The questionee knows they're not going to actually let him die. There's no actual threat of death. If the questionee makes this threat up in his mind, that's not our problem. We're just making him "uncomfortable".
“If the questionee makes this threat up in his mind, that’s not our problem.”
Except for the fact that the procedure is specifically intended to “make up that threat” in the subject’s mind, and, more importantly, in the subject’s body. The procedure is not merely designed to make the person uncomfortable, it is designed to make the person (and the person’s body) believe that they are about to die. It creates the exact same physical response in the subject’s body as if the subject was actually drowning.