A mental state was a state of mind.
In 2268, while confined to the brig of the Romulan flagship, Captain James T. Kirk's condition was described by Doctor Leonard McCoy as mentally depressed, physically weak, disoriented, displayed feelings of persecution and rebellion, and not fully competent. The Romulan commander deemed that because of Kirk's mental state, he was unfit to continue in command of the USS Enterprise. (TOS: "The Enterprise Incident")