The Fifth Circuit has determined that an Immigration Judge need not consider a petitioner's post-traumatic stress disorder when evaluating credibility, unless the petitioner has been deemed incompetent or have a mental illness or serious cognitive disability that affects their ability to provide testimony in a coherent, linear manner.
The full text of Singh v. Sessions can be found here:
http://www.ca5.uscourts.gov/opinions/pub/16/16-60059-CV0.pdf