Don’t Worry, Be Happy? Please.

Why, when something potentially terrible may happen, do people say to the person to whom it may happen or whose life it may affect, “Don’t worry”?
“I just got tests back from my doctor’s office and there’s something wrong with me but he doesn’t know what. He told me to come back for a scan. He wasn’t smiling when he told me.” Oh honey, try not to worry.
“My puppy has an ailment that we can’t quite identify yet, so the vet has to do more tests.” Don’t worry, baby. Try not to worry.
Yeah right. Don’t worry. Don’t worry, be happy. Don’t worry, don’t think about it, blah blah blahhhhhhhhhhhhh.
True, worrying won’t change the outcome of anything, and it may sap your energy and distract you from more important things in your life, like the job you hate and the Christmas pollyanna and all the other pressing hoo-ha, hullaballo, flotsam, and jetsam, but fuck it. I say WORRY. It won’t do any good, no, but at least you won’t be pretending you’re not worried.
Worrying means you care.
Don’t worry. Yeah right. I’ll gnaw my fingernails to bloody stumps, churn my stomach into a burning acidic mess, and punch and kick walls until my knuckles bruise and I can’t walk.
But don’t worry about me. I’ll be fine.
P.S. No, nothing is wrong me and/or my dog, thank god/whatever. Really! So … don’t worry.