This one works extremely well for me:


Put your lips together, with a very small opening in the front. Breath deeeeeeply, sucking the air through that opening like you're drinking a milkshake, completely filling your lungs, then let the air out the same way expelling it 100% (I don't mean kill yourself trying to empty your lungs though). Just keep it up till the anxiety has diminished, it should work pretty well.

Oh, and if you drink coffee I suggest you quit that, it really makes anxiety worse.