I know it sounds really strange, but when my buzz gets out of control I grind a small palm full of black pepper, and take a slow, deep whiff of it right next to my nose. .. I'm not joking, I'm a skeptical person in general but I'm prone to panic attacks so I've tried all kinds of stuff (within reason) without much evidence. I wouldn't presume to know how, but it's literally never failed me. I do breathing exercises for anxiety anyway so it isn't just breath regulation. It also doesn't seem to help with non-cannabis related anxiety. Worth a try in any case!