Walking meditation is also helpful during a panic attack. I know it's hard to get out of the house, but fresh air is good for us, and it's also good to use our peripheral vision --most of us overuse our focal (reading) vision with all the electronic devices we own.
Be sure to use soft focus while walking and looking at your feet. Soft focus helps activate peripheral vision, as does noticing what is happening in your peripheral vision.
Another big help is to fit in some high intensity aerobic exercise regularly (during non-panic attack times is best I find.) Think of being calm as like having money in the bank, and being stressed as like withdrawing money.
High intensity aerobic exercise (provided your doctor okays it) puts money in the bank so that you don't overdraw your account and go into panic attack mode. Dr. John Ratey discusses how effective this is to reduce anxiety in his book Spark.
Other things that add to your bank account of calm are yoga and meditation.