I would (and still do actually) sometimes plunge into a deep funk without any obvious trigger. Particular fears or anxieties would just surge up and it would be out of my control and not related to any current action or behaviour by my WS. So there's that, but that's not to do with triggers as such.
As far as triggers go, they have diminished a little. Initially they were everything everywhere. I think there are two broad categories for me. One is the stuff that relates to the emotional loss, the connection my WS formed with someone else. So things like love songs, rom coms, attending weddings, etc are just things I can't go anywhere near without pain and being reminded. The other category is more connected with the gaslighting and the need to reassess memories in light of the new information. I think those are worse (and probably how bad they are depends on how long you were gaslighted for, for me it was a year and a half which covers a lot of ground), but on the other hand your psyche seems to be able to work through them piece by piece. These, for me, have basically been everything everywhere. Every time I load the dishwasher - this one has never passed - I am triggered by the memory of seeing two coffee cups in the dishwasher when I loaded it during the affair. I would always see the two cups, pretty much every day, during the affair, and think, right so he was here again today for a coffee
(To be clear, I honestly just didn't think she was cheating. In retrospect it is all very obvious but that's how gaslighting works, when it's someone you trust absolutely. So I would have all these annoying thoughts about how she had elevated this "friendship" with a neighbour but never thought it was anything other than a friendship. This is even though there is a huge, really long list of obvious signs in retrospect. The fact that he also pretended to be my friend adds to the confusion. In short anyone looking from the outside could have said, "dude, wake up", but the one thing I always thought about my wife was that she was a person of very strict honesty and loyalty and it never even appeared to be a possibility to me that she would lie at all, much less lie a million times a day for 18 months, risk our children's welfare, etc.)
The dishwasher is just a random example, to show how mundane triggers can be. The thing with the gaslighting is that virtually every single memory needs reassessment. If there was a Christmas during the gaslighting period then you are going to be triggered by Christmas. For me, given it went well over a year, that means every occasion. Our in-laws do a similar thing every year for various kids' birthdays, so every one of those takes me back to being gaslighted. You basically are suddenly hit with a full year or two year's worth of deeply traumatic memories, all at once. Every moment of every day of every week of every month becomes a traumatic memory, a 10 out of 10 threat level that anyone would respond to with full force, with maximum adrenalin, total focus, etc, if only they were aware of the threat.
The nature of these triggers - what distinguishes them for me from just being reminders - is that they take you right back to the time that you are remembering. They are a PTSD symptom, in effect. There is a huge element of helplessness; you are taken back in memory to a time when you (and your family) were under an extreme threat. You are really right there, feeling the threat in its entirety. It feels (on a physiological level) like it is happening in the present, so your whole system goes into a fight or flight mode (mostly fight for me...) and wants to respond to the threat. But of course the threat is in the past, the situation is not actually there to be grappled with, so you are both ready for fight/flight, and at the same time completely helpless to do anything. You cannot defend yourself or your children or your family, your safety, the safety of your loved ones, at all. You are totally powerless.
These kinds of triggers have diminished for me over time, but there are still quite a lot of them.
Another thing, not so much a trigger, is things like nightmares. The content of my dreams changed completely post d-day and I would frequently have terrible nightmares related to the betrayal, the humiliation, the contempt in which I was held, the danger to my world, etc. I'd be difficult to be with the day after a night of those. I was not yet 45yo on d-day, but my hair is now completely grey (or white really); I should add that the period of the affair was incredibly stressful because of the "problems in our marriage" that I thought were just between us but were still very hard on me (I actually thought our friend, her affair partner, might be someone she was confiding in, and that given he had a 20-year marriage and small kids, he might be talking her through working on our marriage. omg). I have had extended periods with such tightness in my chest, my gut, so much bodily tension, lack of sleep, just all kinds of physiological responses to the stress and sense of imminent harm, that I am 100 percent certain I have lost years from my lifespan. Unless something else gets me first, I am pretty sure I'll die of a cardiovascular cause and it will be much earlier than it would have because of the damage this has done to my system. The upside is that life is so flat and joyless now that I will care a lot less about that day coming than I would have before.
As with PTSD, you also become hypervigilant. Small things can seem more threatening than they really are. You can appear to be overreacting. On the other hand you could just be more switched on; in the year after d-day I was first on the scene to break up two real fights in public places. In one of them I was waiting for a coffee and observed something that looked slighly off outside. Then I saw one of the people throw a punch at the other and literally before the victim hit the ground, I had run out there and was right in the face of the guy who threw the punch. I have no recollection of the run, just of seeing the punch thrown and then being in the guy's face. I didn't think about it at all so there was no element of fear at all. It was when I told my counsellor this story that she pointed out that I probably have PTSD, hence becoming hypervigilant. To that I would add a tendency to just do whatever needs to be done without really thinking about the risk to myself, which comes (I think) partly from feeling much more strongly about "rightness", partly from almost hoping to have an excuse to beat someone senseless, and partly from not really caring about risk to myself any more since I have so much less to lose.
Sorry, I have rambled a little but I hope this all relates sort of broadly to the total impact, not just triggers but some of the other things that are a bit like triggers in terms of changes in personality/behaviour.
One more thing... during the post d-day "crisis" period, there's a big part of you that tends to be focused on just restoring the pre-affair reality. It's sort of a form of denial, maybe not part of conscious thinking but at least a strong thread in how you are operating. I often think of this (true, I am told) story of this car driving down the road, and the driver has his arm out of the window as people used to do. The car went past a pole and the driver's arm was literally ripped right off. The car continued straight along the road for another few hundred metres before suddenly swerving from side to side and crashing. The point I get from this story is that we humans sometimes take some time to recognise the full scale of a sudden drastic change. Our initial response is to maintain the previous version of what seems safe and okay. We are driving down the road and our arm gets ripped off, and we take a little time to fully grasp this. For a moment our system says, "something has happened, not sure what, must drive straight." So we don't crash straight away, we crash a few hundred metres down the road.
While we are still in the chaos of "wtf is even happening??" post d-day we are in a fairly simplistic state, trying to keep things together, keep things from falling apart further, preserving what we've got without taking stock of it. Once the affair is over, the immediate danger has past, and things are on a slightly more stable footing, THAT is when the reality really kicks in. That's when the driver realises his arm has been ripped off, that's when the car starts swerving, that's when the crash happens. For me there is a big element of "be careful what you wish for" in the post d-day period. It can feel like if you can just get your spouse back then you will have gotten over the hard part and start the positive work of reconciliation. In fact though, the hard part starts when your spouse comes back. The affair and d-day are not as hard as reconciliation is, because during reconciliation your whole self begins to reengage with your situation. During the affair and the immediate post d-day period, most of your system is shut down because you are just running on your danger responses, in crisis mode. Your analysis may be detailed but at the same time it is superficial; your full set of emotional responses and your full process of dealing with memories kicks in only later, when the dust has settled.