Normal people... Something hits hard, they take a few months, work shit out, & come around.
That's not how PTSD works. It's cyclic, and even though it's incredibly manageable (compared to most disorders), when the dark hits? It hits. Hard & fast, usually, although it can creep in like a freezing fog, too. Anniversaries, ugh. For most vets I know that's anywhere from a few days to a few weeks of hard times. A lot of us have stacked anniversaries, most of mine are in the fall. Which, yeah, means I'm a mess for most of every Autumn. Even during my good years, when I had about 92% of my symptoms sorted, I'd have a run of insomnia & shortened temper every fall. During my bad years the Autumn is a complete clusterf*ck of anxiety attacks, nightmares, self loathing, & worse. Stacked anniversaries can mean months of "Cheque Please! Make the world stop, I wanna get off?" (Similar to being a "hunting-widow" for our partners.) Knowing about anniversaries in advance is more for being able to batten down the hatches & wait for the bad blow to run its course than about avoiding them.
Honeymoon periods in relationships tend vanish or minimize most of our symptoms. Then stress hits, and bam! Welcome to the roller coaster. Sometimes it's extreme, sometimes it's subtle... But we're always on it.
Whether that's something you can deal with? Is a very personal thing, and there's no wrong answer. I've generally found that there are basically five kinds of blokes I've dated in regards to my PTSD. Those who love it*, those who like it, those who are unaffected by it, those who dislike it, and those who hate it. The first 3? Are doable. The last 2? OMFG. No. Just no. They're either martyring themselves, or gutting themselves, or furious at me, or constantly trying to fix me... Or more commonly some unholy combination of the above. The absolute worst is when they lie about it. When they know up front that this is something that shreds them or infuriates them, and they try to hold on because they like "me" so much. Nope. They like symptom-free me. Actual me includes the dark times.
* When I say I've dated blokes who love my PTSD, I'm not talking about dating assholes who love that I'm hurting. I'm talking about dating men who love how strong I am most of the time, but then they still get to be my hero & strong arms when I fall apart. They like rousing arguments or being the cool voice of reason when I'm pissy, and changing plans, and moods changing on a dime, and a whole lot of "you're never boring". They like their independence and being able to take off for alone time when I'm isolating, or that I "get" isolating and don't take their shit personally since I do it myself. A whole bunch of stuff. Like hunting-widows who love that from the start of the season to the end? They're having girl's nights, and painting parties, and super independent months of their own sans-spouse... Versus those who feel used, abandoned, hurt, unwanted, furious, etc.