The stench of this house of death was nauseating. The thought must have come to his mind he was nothing more than fodder, a night time snack in the belly of a hungry sea monster. He had been saved from drowning and now he desperately needed to be saved from digestion, because it's a very real danger. The animal was so enormous that his tongue alone was the size of a hippopotamus. Jonah's skin must have tingled there in the dissolving liquid.
Stomach acid is potent stuff.
It must have seemed that he was being slowly but surely reduced to Whale fuel. Enough fuel to provide a mile ot two more for the travels of this monster. As time went on he must have seriously wondered if his prayer would penetrate through the walls of this prison chamber before the gastric juices penetrated his skin. The book of Jonah proves that. You see, what could happen more to Jonah would be a failure of god.