MD11? Loaded too far forward, maybe. But never loaded too far back. She'll pop a wheelie way before things get dangerous.
Happened to a friend of mine on a quick turn in KSEA. The rest of the crew went in the office during the loading, but he stayed in the RFO seat to grab a quick snooze.
He said as he closed his eyes he was looking at the lights of the ramp and cargo facility. Fell asleep, woke up and looked out to the moon and stars. No one had tethered the nose. Thankfully the tug was hooked up so the towbar kept him from ending up all the way on the tail....