I've got this app on my phone that times the breathing. I've been doing that for about two years now and it really helps, especially when the anxiety is "acute". Like one time I was barely sleeping and I started doing the breathing and went from zero sleep to about 5 hours. It takes a while to get used to and can be a bit uncomfortable, but it's the most helpful non-drug thing I've found in 20+ years.

This is the app: http://www.saagara.com/apps/breathing/relax