The caller -- who owns one of the cars Loney hit in his silver Maserati -- describes the entire incident in suspenseful detail ... WHILE IT'S HAPPENING.

When the person on the phone makes the call, she says Loney is "'completely passed out in the front seat" after colliding with several cars -- but Loney wakes up before she ends the call, and tries to take off.

The caller freaks out -- screaming, "Oh my god! Oh my god! He tried to leave the scene ... He woke up, and he slammed on the gas and took off across all the lanes on the freeway."

The caller says Loney quickly hit another car and ended up on the other side of the highway with a broken axle. You gotta hear the clip.

As we first reported, cops handcuffed Loney on the scene and transported him to a nearby hospital for evaluation, where he was later arrested on suspicion of DUI. Cops say they obtained a blood sample to test for drugs -- but it came back negative.