Is one who masturbates, not out of lust, but to excrete urine retained due to a psychological illness that has affected his health, considered a sinner or blameworthy?

You must consult doctors to solve your problem and not resort to masturbation, for Allah Almighty has not made our healing in what He has forbidden to us. What you have done is not permissible, and you must resort to treatment through permissible methods.