"August: Osage County" actress Misty Upham has been reported missing in Washington ... and her family fears she may be suicidal.
The actress was last seen walking by herself from an apartment Sunday near Auburn ... and her dad says Misty told them she was going to visit friends.
Her dad told the Hollywood Reporter Misty had been dealing with erratic behavior and recently changed her meds. He says when they last spoke Upham told her parents they didn't need to worry about her anymore.
That's when he got nervous and contacted police ... he was worried she might kill herself.
Cops say they've responded to 4 suicide calls at that apartment in the past year ... including one on the day she went missing when her dad called -- but when they arrived, Misty was gone.