1.) You need to change your POV.
If you're the dumpee, I think it's important to see things from the point of view of your (ex) SO. If you're the one doing the break-up, you need to really understand why you're doing what you're doing. I was in a relationship for almost a year, so I wasn't breaking up with said person for a silly reason. A lot of emotions are going into that break-up, and you need to understand why things are happening the way they're happening.
2.) The whole world is going to know.
You can keep it to yourself, but you can't control what the other person does. In a matter of minutes, a ton of people knew. You're allowed to be upset over this because it's something private. I don't share my intimate details with the world, and I bet many of you don't either.
3.) You can lose or gain weight.
I ate my feelings, something that was a first. I usually lose my appetite when I'm sad but I found myself crying into a slice of cake one night while wishing I could make another cake. I kind of felt gross by the end of the week because I had been eating so much junk food.
4.) You get treated differently.
I was pretty okay the first two days and my parents were freaked out. They were watching me, talking quietly, and asking me how I was feeling just about every thirty minutes. My friends had to push me for details because I didn't want to talk about it. Any my co-worker kept asking me if I was sad and when I planned to start hooking up with strangers so I could join him on his wild nights.
5.) It sucks.
How can you go from speaking to someone every minute of every day to not at all? The silly trope in TV shows when someone sees something small that reminds them of their ex and sends them spiraling, that's true. I passed a target (a place we visited whenever we were bored) and instantly had a lump in my throat.
6.) It's okay to cry.
We all handle break-ups differently. I wanted to be alone, but others will want to be with their friends and family. Whatever it takes to start feeling better, go for it.