Every human has cried. If all is well, we start crying after birth. So, it is completely natural to cry. It is a way to releases pent up emotions, and it informs others of our state of being.
Children cry in order to communicate their needs to their parents. Without this tool, they would be helpless. So, why is there a stigma around crying when adolescents and adults are involved?
Language is useful for many things, but sometimes emotions are too complex to explain with words alone. Sometimes a person gets so overwhelmed, to the point where nothing makes senes. Everything is incomprehensible, and the only way to express oneself is through crying.
When I am overwhelmed, I cannot control my ability to cry. This usually leads me to take a break, or if I am stubborn, lets someone who cares know that I am not well. From both outcomes, I am forced to acknowledge my feelings. From there, I can find the cause of my stress and combat it.
There are many scientific studies on crying. And to summarize them all would be impossible. So to start you off, I recommend that you acknowledge that you have emotions and that your understanding of them is vital to your mental and physical health. You should remind yourself of your needs, whether they are physical or not. I also suggest you read the linked articles if you want to learn more about the subject.