It's much more common that the red line is slowly but steadily diving to the negative side on the graph. ♦
In micros it's somewhat difficult to get that red line climb even to zero because to do that, you have to bluff quite often and in micros those bluffs don't necessarily work that well.
One other major reason why that red line have tendency to "dive" is blinds.
Sample isn't that big either, so especially if you've been playing with really weak-tight opponents, the red line almost automatically goes up because you can easily steal pots.
So i don't think that you should be worried about it.