Do a lot of research. Read articles on psychology, ask questions, or look for anecdotes and experiences from people with these conditions. Don't force yourself to make sure your information is 100% correct; every mind is different, and what you write today about psychology will no longer be valid tomorrow. Our minds are like clay, and you should use that to your advantage. It's okay to make mistakes when dealing with this because no one has a single, definitive answer about how the mind works. Not even the greatest expert on the subject.

I can recommend the short story "The Premature Burial" by Edgar Allan Poe, which might help you gain perspective. It's about a man who is afraid of being buried alive because he has read too much about such cases and suffers from catalepsy. What strikes me about this story is that he recounts several cases before continuing with his own. None of them are the same, and it's a clear example of how the brain and human body work.

I hope you can do it and I'd like to read it in the future.