South Australian Liberal Senator Mary Jo Fisher says her battle with depression left her feeling out of control and in the "depths of despair".

The senator told her shoplifting trial in Adelaide that she sometimes felt hopeless, inadequate and not up to her job.

Her physical symptoms included sweats, flushes, trembling, an inability to focus and nausea.

"Basically I wasn't in control," she told the Adelaide Magistrates Court today as she gave evidence in her defence.

Senator Fisher, 48, said the problems began in early 2009, though in hindsight she probably should have sought help from about 2004.