Issac's girlfriend died, he had to fight terrifying creatures that looked like corpses, he got dementia and PTSD from being in touch with the marker. He had a hallucination of his dead girlfriend telling him to kill himself, had to kill toddlers that turned into monsters, he had to stick a huge needle in his eye, and he had to accept the fact that his girlfriend was dead, and is never coming back
And not to mention, his subconscious tried stabbing himself in the eye with a needle
AND when the space station he was on was exploding, he just sat down and would rather die than try to escape, because he was so okay with being dead