This situation is mainly due to the wrong way of breathing, plus insufficient exercise and insufficient vital capacity. These reasons will cause you to breathe insufficient oxygen through your nose when running. At this time, you need your mouth to help you breathe. Looking back, do many people unconsciously open their mouths and breathe in the later stage of exercise?
When you breathe with your mouth open, because the capillaries in your throat are exposed, some particles in the air rub against them, which will cause the capillaries to rupture and make you feel bloody in your mouth. Sometimes mucosal bleeding can also produce such a situation. Don't worry too much. It's okay to have a rest. If you feel the smell of blood, you can drink some water, but not too hot and don't irritate the capillaries.
In private, most schools (including some colleges and universities) ignore students' usual physical exercise, and it is not good to suddenly let students start running when it comes to physical fitness test. After all, there are still some risks in this way. Carelessness will affect students' health.
But then again, students, health is the capital of revolution. There is a lot of time in college, so why waste it on less important things? Games, novels, TV plays ... are those things really worth staying in the dormitory all day?
Do more exercise if you have nothing to do. Go to the playground for two laps (jogging is enough, no overload), you will feel very comfortable and breathe a lot easier ~