I'm writing an elementary gravity simulation where a square falls to the ground and bounces with damping. However, after a few good bounces, the square seems to get 'stuck' in the floor - it does not rebound with the expected impulse. After this happens, it continues to do little mini-bounces in the floor, but without damping. Why is this happening? This code:

//Initial position
float x = 100;
float y = 0;

//Initial speed and constant acceleration
float speed = 0;
float gravity = 0.5;

void setup() {
  size(200,200);
}

void draw() {
  background(255);
  fill(0);
  noStroke();
  rectMode(CENTER);
  rect(x,y,10,10);
 
  y = y + speed; //change in position
 
  speed = speed + gravity; //acceleration
 
  if (y > height) {
    speed = speed * -0.8; //damping upon rebound
  }
}

Thanks :)