Ex-New England Patriots star Aaron Hernandez just took the witness stand for the first time in his high-profile murder case ... and told the court he's not mentally ill.
During the hearing, the judge peppered Hernandez with a barrage of questions about his overall health and mental state. Hernandez -- who was pretty composed on the stand -- insisted he's A-OK.
Hernandez has pled not guilty to the murder of 27-year-old Odin Lloyd.
If convicted ... Hernandez faces life in prison. When asked if he understood the gravity of the situation, Hernandez told the judge he got it.