When you train, you might have some bad habits. If you do not fix that, that will affect your fighting skills. When you punch or kick and move your head here and there, you need to stop moving your head like that. It is not going to help you later. That's a bad habit.
You might not realize that and you think you are doing it right. That's why, I always recommend learning martial arts from martial arts instructors who can show you what you are not doing right and how to fix that.
You might think it's okay to move head like that. You can watch this video where it shows how your head might move. if you move your head as a defend so that your opponent misses his strike. That's different thing. But in case your head moves automatically, you should pay special attention during your training.
One thing you can do to stop and correct that is practice in front of the mirror. You can see yourself in the mirror and fix your moves.
Thank you so much for reading this. Please feel free to share your thoughts in the comment section. Stay safe. Always be happy!