Settle down!
If someone tells you "Settle down!"
it means that they want you to become less upset, less excited, less
frightened, etc. In other words, they want you to become less emotional.
Telling someone "Settle down!" is
very direct, so it's rude if you say that to someone who you're not close to.
(someone) gets worked up
"Getting worked up" means becoming
emotional about something. The emotion is usually a negative one like anger or
worry.
Sometimes people use "all" in this
phrase:
Look, you're getting all worked up again. I told you to relax!
(someone) gets worked
up over nothing.
This means that this person was upset without a
good reason. Use this phrase when someone gets worried or upset about a
problem, but that problem solves itself or disappears.
For example, imagine that a family member was
really worried that they had a disease. They got a test done, and the test said
that they were healthy. You can say:
See? You got worked up over nothing.