From "Star Trek: Turnabout Intruder (#3.24)"
She is suffering from the delusion of being Captain Kirk.
James T. Kirk
[in Janice Lester's body
] I am NOT Janice Lester!
The paranoia has been developing for the past six months. The radiation seems to have intensified it. She must be kept sedated.
Nurse Christine Chapel
Shall I prepare a mild sedative, Doctor?