Getting my character to slide 2D platformer

Hello I am having trouble having my player slide properly. When the key command combination is pressed he almost instantly teleports to the new location (which is no where even close to what I want him sliding to - he is short about what I would say 50 pixels) and the slide animation does not trigger.

 void FixedUpdate ()
     {

/OTHER CODE COMMENTED OUT TO SAVE SPACE */

         if (Input.GetButton ("Down") && Input.GetButtonDown ("Slide"))
         {
             isSliding = true;
             if(transform.localScale.x  == 1)
             {
                 rb2d.mass = 0;
                 rb2d.AddForce (Vector2.right * speed);
             }
             if(transform.localScale.x  == -1)
             {
                 rb2d.mass = 0;
                 rb2d.AddForce (Vector2.left * speed);
             }
             timer = 0;
             timer += Time.deltaTime;
             Debug.Log(timer);
         }
 
         /*
         if (Input.GetButtonUp ("Slide")) 
         {
             rb2d.mass = 1;
             isSliding = false;
         }
         */
 
     }