"I woke up from a nap SO fast, I whacked my face on a table," she wrote, adding the hashtag "idiot."
In another photo, the former Bachelorette posed with a small bandage close to her eye and joked that the injury would cause problems on set of Home and Away.
"The show's continuity dream. A random unexplained black eye. Sorry team," she wrote in the caption.
Sam first gained popularity appearing on The Bachelor in 2014. She was chosen as Blake Garvey's winner, only to be unceremoniously dumped by the Bachelor for second-runner up Louise.
A year later, Sam appeared as Australia's first ever Bachelorette.