What Could Viewing Abnormal Shadows Around Headlight While Driving Indicate?

i am a professional driver, when i am fatigued at night sometimes i see shadows that arnt there just at the edge of my headlights. when talking with a coworker he also sees experiances this. we both see them comming from the left side if the road, just at the edge of the headlights, and upon registering this mentally we look for whatever it is and nothing is there, i thought i was experianceing this personally, but now i am wondering if this is a common phenonema and if there is a name for it