First off, I'm not much of a game developer so this question is probably in the realm of "How do I facebook my google books".
I noticed that if I have a bullet fire at an angle of 90 degrees, instead of the bullet going straight up it actually goes straight down. 0 still goes right and 180 still goes left, but 135 goes to the bottom left instead of the top left. It seems the angle of degrees has been flipped upside down.
Is there a reason for this? Is it something specific to video games?