Whilst I understand the point you're trying to make, which is valid and as you said comes from a place of kindness, it's not helpful to tell people with acute anxiety to "just relax". It doesn't work like that. There's also nothing unnatural about anxiety, it's essential for life, it's what stops us doing dangerous shit that might get us killed. It is however complex and often illogical and we all deal with it differently.
I don't mean to preach but I speak from both my own experience and struggles with anxiety over 30 odd years and from my professional experience working for an NHS Mental Health Trust.