the fall and weightlessness

I made using command blocks mechanism and created an artifact which you can use to fly (levitation) and but when I served, even with a height of 4-6 unit I damage very high damage depending on how many times I applied to the air, I expected that I would be the damage to 1 heart or half is applied at 3-7 and more. to see this error you must do the thing which will cast a levitation (3 seconds), to fly and to fall, but to have time to levitation and fly again and so 3 times, then fall from a height of 5 units.