I think the best way is to prepare and prevent, rather than cure when acute symptoms occur. This person should stimulate the acupressure points regularly on daily basis.
Plus, I'd suggest creating some sort of relaxing anchors (NLP term) beforehand. Meditation can do wonders, too. During attacks it's important to concentrate on the breathing and make it slow, deliberate and deep.
I've also seen an awesome and simple technique... The person should have and elastic around the wrist. When the symptoms begin, he/she can break the state by simply pulling and releasing the elastic, experiencing a light pain on the wrist when the elastic hits it. This can also be an anchor for calming down and relaxing he/she created beforehand.