Ethan went through a lot of psychological trauma due to Jason's death along with him being injured in the crash which would supposedly lead us and him to suspect Ethan to be the killer.
Yes, Ethan had a blackout when Shaun disappeared. But I do believe he had blackouts after that aswell, or before, can't remember.
As for where I got this from. I have had discussions about Heavy Rain with my brother, so I guess from my own and his mind. Do not know where he got his information from though. Or what were you refering too? The explanations for Ethan's blackouts and Madison's PTSD?
http://www.youtube.com/watch?v=jxpdGB6Gbac Explanation for the blackouts/PTSD