I think it is very, very natural that overcoming major obstacles goes hand-in-hand with feeling like the Sword of Damocles is hanging over your head long after the actual obstacles are gone. Why? Because most of us have the privilege of living in a soft, fuzzy cocoon of denial. Bad things happen to other people, right? And whenever we see a story about something bad happening to someone else, we can almost always rationalize how in some way they brought it on themselves, or that they were subject so some particular situation that doesn't apply to us. So of course those bad things won't happen to us, because we are smarter, or luckier, or live in a safer area, or whatever.
But when really bad shit actually happens to you, it completely rips that veil away. You are forced to realize that sometimes bad shit happens just by sheer chance or bad luck, despite all of your best efforts. And when that veil is ripped away, you can never really, fully replace it. Because if bad shit happened once, there is absolutely no reason on God's green earth that it cannot happen again. Or that even worse shit won't pile on top.
Look, I had several miscarriages, despite having done everything "right" in my life up to that point. The first one was a sad stroke of bad luck; the second felt like a trend, and evoked an icy-hot rage like I had never felt. Even when I managed to hold onto a pregnancy, I spent the entire rest of the pregnancy expecting to lose the baby, and the first solid year of her life expecting something horrible to happen to her, like me falling down the stairs, or a car jumping the sidewalk and running us both down. Because that stuff can and does happen, and I am demonstrably not immune -- so what's to keep it from happening to me again?
I think the only thing that can really help with this is therapy -- you have to find a way to break the mental cycle, that little voice in your head that gets triggered by some event or some conversation and slowly convinces you that you're going to end up back on the street. I learned to fight it by basically arguing with it -- the nasty lady in my head would say "you know you're going to lose this baby," and I'd say, "well, then it's a good thing we have the resources to do IVF if we need to"; she'd respond, "yeah, right, you know you're never going to be able to keep any baby," and I'd say. "well, then it's a good thing that we have the resources to adopt." Etc. ad infinitum. It was my own personal version of CBT before I knew what that actually was, just fighting those negative thoughts by pointing out to myself, every time, how silly and self-defeating they were.
The other thing is this: bad shit is either going to happen, or it's not. If it doesn't happen, why would you want to waste your time worrying about something that wasn't there? If it does happen, then why would you want to suck the joy out of the good years that you do have fretting about something that you can't change or avoid? I realized after a couple of years that I hadn't really enjoyed my pregnancy or even the first year or so of DD's life, because I was so worried about what might have happened that I missed a lot of the wonderful stuff that was right in front of me. What good is having two wonderful kids if I can never enjoy my time with them -- if I spend their entire lives waiting for the other shoe to drop. So, what, I finally relax on my deathbed, because I successfully kept them alive my whole life?* Carpe some damn diem, you know? You worked your ass off to get where you are, and you have proven to yourself that you have the skills to do it again if you have to. So you deserve to enjoy and appreciate the good times for as long as they last, knowing that you can handle whatever happens next.
Tl;dr: You are a badass. You have to be to have gotten where you are. Because you are a badass, you can handle whatever comes next. So give yourself permission to relax and enjoy what you've earned.
*Yeah, right. At that point I am still fretting, because now I won't be around anymore to protect them from future bad shit.
