Saxby Chambliss, Senator from Georgia and VP of the Senate Intelligence Committee, gave additional details of the raid on Bin Laden's compound. From those facts it is obvious that Osama Bin Laden knew that American commandos were closing in and that he was in the last minutes of his life.
The commandos killed two people on the first floor of the three story mansion, and were using explosive charges to open sealed doors. On the third floor, where Osama sat cowering in his bedroom, the commandos blew open a sealed door to reveal a hallway. Bin Laden's bedroom was at the end of the hallway, and he poked his head out to see who was coming for him. One of the commandos fired a shot at Bin Laden but missed. Osama therefore got to enjoy the feel of a bullet whizzing by his head in the last few moments of his life. Seconds later, the two commandos entered Osama's bedroom and shot him to death.
See Chambliss's account here.
I remember seeing photos of people looking out the windows of the World Trade Center, knowing there was no escape. Many of them jumped to their deaths rather than wait to be burned to death by the flames. These victims of Bin Laden had ample time to contemplate their fate. Unlike Bin Laden, they never knew who had attacked them or why they had to die.
Bin Laden was lucky. He died relatively quickly and probably painlessly. Unlike his victims of 9/11, Osama knew who was attacking him and why. Somewhere in his consciousness he had to know that it was payback, that he had brought his fate on himself.
No doubt he felt the terror of his impending death, but not for long. Not nearly long enough.