Stewy, this will sound simple, but it works. I need this and use it and it works.
Belly Breath: Breath in and allow the air to fill up your tummy until it expands a bit. Then, exhale slowly through your mouth using your belly to push the air out. If you do three of those in a row, you will calm down. The thing about anxiety is that your breathing automatically becomes shallow and quick and that makes things worse. You can do this!