Justin Bieber can't keep himself out of trouble. Right after posting an inspiring video about getting back up after a fall -- literally -- he's taken another public stumble, and this one could have been deadly. An ambulance was called to Bieber's mansion. What happened?

From the sounds of TMZ's report, a lady guest of Bieber's had a bit too much booze and passed out. His security team called the fire department dispatch and requested that a private ambulance to come retrieve a 20-year-old (read: underage) girl, and alcohol is said to be a factor in the debacle.

However, about 15 minutes later, the ambulance was called back and told they weren't needed. Apparently the girl woke up and insisted she didn't need medical attention.

TMZ noted that the incident went down at a party at Bieber's Calabasas mansion -- and that they're not sure if any other substances were involved in making her unconscious. Uh, yikes!

We're glad she's okay ... we just hope nothing scarier happens again. Be careful, Biebs!