I find that people will freak out even if you lead a sentence with "Don't freak out”. So I've started normalizing it by adding it to routine conversations.

Don't freak out, I approved your expense report.

Don't freak out, your haircut looks good.

Don't freak out, the 5 year old locked himself in the trunk again.

Don't freak out, what should we have for dinner?

See? It works.