Well if it's any help, in Construct 0-degrees means something is pointing to the right, and then the degrees go upwards in a clockwise direction. So if you're traveling to the right, a number between 0 and 90 is going down, and a number from -270 to 0 is going up a slope.
In the Line Rider game you could also slide backwards, though, and it wouldn't change which way you were facing. In that case, traveling left while having an angle of -270 to 0 would still be on a downward slope!
So in that case, in your events you first need to determine if you are facing left or right, then you need to determine if you're MOVING left or right, and THEN you have to find the angle of the slope to figure out if he is going up or down a slope.
I'm new to construct myself, so this is the only thing that popped into my head, haha.