Does telling someone to calm down ever work?

[NewMatress]

I'm in a very high stress situation. Having to deal with professional people who are supposed to be there to help but often can't, sometimes because there's genuinely nothing they can do, I accept.

This morning has been particularly stressful and frustrating and I'm sure that was coming accross in my tone but nowhere near as bad as it was after I was told I needed to clam down!

No it makes me more angry /stressed

Yes. I'm aware that I'm not always aware when I'm being irrational, and being told can make me stop and think.

It can do.

I know someone said it to me, when I thought I was being rational. Because I trust them, it made me think and realise that actually not only was I being very irrational but my behaviour was exacerbating the situation. I'm generally calm over most things, so my behaviour was out of character too.
I took it as permission to take 5 minutes break, came back and apologised (and so did they )and then we managed to get everything sorted far quicker and better than we would have otherwise.

Yes, it can be done in a patronising way, or in a deflecting manner-to turn the issue from the actual issue to you being a problem, but it isn't always.
Sometimes a bad situation can be made a lot worse by having someone who isn't calm taking it out on everyone else, especially if there's nothing anyone can do at that point.