Robert Carradine's Medical Examiner Report Reveals Tragic Details About Death

Robert Carradine, the actor best known for his roles in "Lizzie McGuire," "Revenge of the Nerds," and "The Long Riders," had been battling bipolar disorder, severe depression, anxiety, and recurring suicidal thoughts for roughly two decades before his death, his daughter told investigators after his tragic passing ... TMZ has learned.

According to the Los Angeles County Medical Examiner's report, obtained by TMZ, the actor's daughter told investigators her father had struggled with mental illness for about 20 years and had been diagnosed with bipolar disorder. The report also notes he suffered from severe depression and anxiety and was taking multiple medications.

The M.E.'s report states Carradine checked himself into a Los Angeles psychiatric hospital where he had previously received treatment because he was experiencing ongoing suicidal ideation.

According to the report, an employee went to Carradine's room the following day to tell him his daughter was on the phone. That's when he was found hanging and unresponsive.

The report says Carradine was in cardiac arrest when he was discovered. No suicide note was found.

Medical personnel attempted to resuscitate him before he was transferred to an intensive care unit. Carradine ultimately died weeks later, on February 23.

As we reported ... the Medical Examiner ruled Carradine's manner of death a suicide. His official cause of death was listed as a brain injury associated with hanging.