50 Cent was hospitalized with possible injuries to his neck and back in a frightening car crash involving his SUV and a mack truck ... this according to a website affiliated with the rapper. 

According to ThisIs50.com, it all went down Monday night on the Long Island Expressway in New York City, when a red mack truck rear-ended 50's ride ... and the rapper's SUV "almost flipped over." 

50 was taken to a nearby hospital ... where, according to the site, doctors are running tests on his neck and back. 

Story developing ...