Half-dream like state. They hit around 4-5am, lights and shapes of the objects around the road form faces, animals or other objects. At the same time I still remember I CANNOT fall asleep, so I "wake up" from this after few seconds, it's not long enough to create adangeorus situation on the empty highway. This so for me a signal to start some intensive measures agains sleep though :D I.e. coffee, singing, eating.

And what you describe is called tetris effect :)