Yes breathing can help calm you during your anxiety.
If you're suffering from anxiety then breathing in slowly as in breathing in and out and repeating that while sitting down and relaxing the breathing in and out slowly can help calm you and your anxiety.
If you're having a panic attack then you need to try breathing in slowly and if you start hyperventilating try using a paper bag to breathe in and out.
Although we need to breathe to stay alive it is possible to breathe too much.
When you breathe too much it's called excessive breathing and when you're breathing too much the excessive breathing creates a low level of carbon dioxide in your blood.
That low level of carbon dioxide in your blood is not a good thing because it causes hyperventilation.
Hyperventilation can be caused by a panic attack, severe anxiety or a medical problem, such as bleeding or infection.
Usually nothing serious happens when you're hyperventilating and breathing into a paper bag can help with the hyperventilation.
However if you think something more serious is going on then call 911 just to be safe.