In this thing you will feel that a lot of times. But don't give up. Everytime you need to practice different ways to improve your typing. At the beginning you improve watching only the screen, when you have 50 WPM you feel like you aren't progressing, and now when I was 70 WPM I slow down my WPS to only 60WPM, but that's normal, it depends not only of your skill but also of your feelings. If you are stress, you can slow down your typing. I never gonna give you up.