What do you hope to achieve? If you care for the person, then you will want to help them to relax and to shorten the duration, intensity and frequency of the anxiety attacks.
Will telling them that they are irrational achieve this? How about reassuring them?
Will raising your voice help to achieve this? How about modeling the behavior you wish them to have by being calm?
How about asking them what they need? Ask them what would be helpful for them. Be supportive. Be the strong silent type and listen without judgment. Be there for them. Be a resource.
©2016 Stephen L. Martin
Painting: Exploration of the Source of the Orinoco River by Remedios Varo