This is a common phenomenon for beginners. If you practice for a while, it's because you haven't mastered the method of breathing. Many people are used to breathing through the chest. If you want to play the harmonica without dizziness, you must learn to breathe with your abdomen. The so-called abdominal breathing means that the abdomen should be tightened when playing. In this process, you should be careful not to hold your chest out. Once you hold your chest out, it will become chest breathing. When inhaling, on the contrary, the abdomen will bulge, and you should feel that the gas has entered your stomach. I was not used to practicing at first. I suggest you lie down and catch your breath. Lying down to breathe is abdominal breathing (because people use abdominal breathing when they are most relaxed) to experience the feeling of abdominal breathing.

That's how I started learning harmonica. Since I learned abdominal breathing, I can basically play for half a day. Hehe, it seems to be selling advertisements. Of course, playing the harmonica has a deeper breathing method, but you have to learn it step by step.