Your own good bits
Go back to the housewarming for a moment. At some point your friend asked how things were with you. You said "Yes, all good", and told her about the one project that's going well. You didn't mention the overdraft, the row in the car or the fact that you've been sleeping badly since February. It didn't seem the moment, and besides, everyone there seemed to be doing so well.
In other words, you edited. That's no crime, since it's what people do at parties, and chapter 3 showed how common it is. But it has a consequence you may not have considered, which is that you're somebody else's good bits.
Your holiday photographs didn't include the day it rained and you argued about the hire car. When you mention work, you mention the win. To at least a few people you look calm, solvent and on schedule. Each of those people is holding their full version against your edited one and coming second. The habit is a loop, and you're keeping it going as well as suffering from it.
Jordan's third study has a detail on this. How far friends misjudged a student's feelings depended partly on how much that student suppressed the bad ones. The more the students hid, the rosier the picture their friends formed. It follows that everyone in a circle can be struggling and hiding it, and every one of them can believe they're the only one.
There's a cost to friendship as well, and I think it's the largest cost in this book. When you're keeping score against a friend, you can't be wholly glad for her. There's a small tax on every piece of her good news. You start holding back your own news too. You hold back the bad because it would lose you points, and sometimes the good in case it looks like competing. Your conversations turn into an exchange of press releases. You can know someone for fifteen years on those terms and know less about her life each year.
The way out is to go first with one true thing, and it needn't be a confession. I'd strongly advise against a public post about your troubles, which is only editing of a different kind. I mean telling one friend, in person or on the phone, one thing from the full version. You might say "Work's been rough since the restructure, to be honest," or "We've been worried about money this year."
I can't promise how it will go. What usually happens, I think, is that you get one back. Your friend looks relieved and tells you about her boss, or her father, or the mortgage that keeps her awake. At that point you know something about her life that no housewarming could have shown you. You can't see anyone's full version unless they show it to you, and they generally won't until someone goes first.
The other half of this is how you answer good news. Congratulate early and be specific. Send the message before the dip has had time to settle in, and say something that shows you noticed what it took. My reasoning is simple. Envy pulls you away from the person, and a warm message sent quickly pulls the other way while that's still easy. It also happens to be what a friend would do, and you may be surprised how much of the dip goes once you've acted like one.