Board Thread:General Discussion/@comment-4976518-20140808063123/@comment-35375498-20180422120207

What if Aizen's bankai isn't intended for his enemies, maybe it's complete hypnosis cast-able to himself while being aware and in control of the hypnosis. Maybe that's why even if Aizen is injured, he doesn't even look bothered much because he can control what he feels with his senses. And if you're using an ability on yourself, why scream bankai out loud and reveal a master strategist's tactics.
 * just a theory though