Really hard to tell for me. And even it’s murky what exactly my trigger was. Here’s a long winded example (my case) of why pinpointing a single trigger is very hard.
My whole life I’ve had weird stomach issues that seemed to flare a little bit more when I was really pushing myself, ie. skiing, long distance running, lack of sleep, or very stressful times.
In 2021, I got a flu (or COVID) and my stomach issues have been ever slightly worse since then, and I remember feeling a little off, though I thought it was due to my changed diet.
In 2022, I got infected by COVID (confirmed), and was somewhat sick, mostly stomach symptoms, my stomach symptoms and quick fatiguability lingered for weeks and were still ongoing when I had a really big knee surgery (a couple weeks post-COVID onset).
That knee surgery thrashed me, I mean I was stuck in bed for a month. (I also couldn’t walk so it kind of made sense I was stuck in bed). But my stomach symptoms flared worse than ever before. Over time I improved, I was doing like 10 hours of physio per week and had gotten better.
So for the next year and a bit, I led a relatively normal life, though with many annoying symptoms, and the feeling my health was declining after every physio appointment (which I blamed myself being “deconditioned” for). I did not meet ME criteria during this time as I was going on runs and cross country skiing.
Eventually all the doctors I’d been badgering sent me to a therapist. Me and the therapist seemed to think I should focus on my symptoms less. So I did. And I had an amazing 2-3 months. Where I pushed myself, felt healthier, and ignored warning signs.
Until one day I collapsed in bed and became very severe. I have not improved since. It was only then I started fitting the ME criteria.
But when did my illness start? What was the trigger? That’s a question without a grand answer I think. “It depends”. I usually say COVID, because that was the difference between when I generally felt okay and generally felt ill.