South Carolina Personal Trainer Told Friend She Was 'Scared for Her Life' Before Vanishing

The South Carolina personal trainer who vanished into the woods this week was acting "paranoid" and feared for her life ... at least according to a close friend.

Sondra Campbell -- who says she was a longtime pal of Elena Katherine Moore -- tells TMZ ... they were at brunch May 31 when Elena's behavior raised red flags.

We're told Elena was acting abnormally during the outing ... frequently getting up from her seat and looking around and out the window as if she was keeping an eye out for someone.

Sondra tells us she didn't say anything because she isn't close with the other girls, but at the end of the brunch, she says Elena opened up to her as they hugged goodbye. She claims Elena told her she was "scared for her life" due to unspecified issues and would fill her in at a later time.

Sondra says she missed a call from Elena on June 4 and never heard from her again.

She adds ... Elena is a "strong-minded individual who lifts everyone around her" and would not just up and leave home unless she had good reason to ... telling us she simply hopes Elena returns safely.

We told you about the eyebrow-raising case ... Elena apparently vanished into the woods in Lexington on Thursday after leaving Planet Fitness just after 9 PM. Her husband reported her missing Friday.

TMZ has reached out to Elena's husband, Brannon, and his family for comment ... so far, no word back. We also contacted her adoptive family, though we haven't heard back from them either.