Calling schedules freezes game?

I have a bit of code in which I call a schedule to function updateDot from within updateDot. I set the time to 20 ms, so my animation runs smoothly, but it also slows down the framerate at 50 ms. What happens is the framerate gets progressively worse until the game slows down to a crawl.

I seem to have this same problem in another game I am working on.

Here is the code of the test I was working on to make a pendulum (right now it just goes around in a circle, havent modified it enough so its an actual pendulum)

right under "add your custom code here" is this:

$dot = new fxStaticSprite2D() { scenegraph = t2dSceneGraph; };
	$dot.setPosition("5 0");
	$dot.setSize( "2 2" );
	$dot.setImageMap( dotImageMap );
	$centerx = 0;
	$centery = 0;
	$gravity = 0.01;
	$distance = 5;
	$velocity = 0;
	$angle = 0;
	updateDot();

and here is the function updateDot:

function updateDot() {
	echo("Function updateDot()");
	%circumference = $distance * 2 * 3.14;
	%travelled = $velocity + $gravity;
	%percentCircumference = (%travelled / %circumference);
	%angleTravelled = 360 * %percentCircumference;
	%newPositiony = $distance * mSin(-($angle - mDegToRad(%angleTravelled)));
	%newPositionx = $distance * mCos(-($angle - mDegToRad(%angleTravelled)));
	$dot.setPosition(%newPositionx SPC %newPositiony);
	$angle = $angle - %angleTravelled;
	
	
	schedule(20, 0, "updateDot");
}

What I don't understand is the game goes very smoothly and it seems like its performing all the calculations and updating the dot correctly, but then about 20 seconds later the game slows to a crawl.