Progressive muscle relaxation training is excellent for people who feel anxiety or suffer from problems brought about by chronic anxiety. This beautifully illustrated exercise can release sympathetic "fight or flight" nervous system responses and provide the relief of "rest and restore" parasympathetic function.
Alternate nostril breathing is a 3,000 year old practice that uses breathing to balance the brain and nervous system. Studies show that this practice can balance the autonomic nervous system.
A panic attack is caused when a person exhales too much. You might call this panting, but it can be more subtle. This problem can be a result of chronic sighing, shoulder breathing, or even breath-holding. When too much carbon dioxide is lost, the bloodstream will not release oxygen out to the brain, heart, or organs. The brainstem senses this oxygen imbalance and speeds up the heart to get more oxygen circulating. The racing heart starts a panic attack and everything snowballs from there. The key to "reassuring" the brainstem is to exhale SILENTLY through a straw. A few weeks of practicing for 5-10 minutes a day should allow you to stop a panic attack cold with only 7 breath cycles.
Some people find that 14 Hz auditory input is helpful for calm focus. You will likely quickly decide whether this is a good fit for you. Of course, there are more tailored solutions for people who have a brain map. You Tube has additional 14 Hz offerings. This is just a sample.