hello, I am very beginner in the field of video game development and I stumble on a small problem and I would like to know if there was someone here able to help me 
I’m trying to make a simple little game where the player must catch different balls of colors that fall using the left and right arrows of his keyboard.
To program the move I based on the basic tutorial “space shooter” of unity but in my case, as the game progresses, the controls are increasingly slow until completely stop without me understand why.
I would like to know if someone had already encountered such problems and if he could help me.
Thank you in advance and good day to all!