Have quite a few that could count, honestly.
First time was probably ~2005-7, I honestly can't remember as I was preschool/kindergarten age, whichever year this was really started my downward spiral. Somehow managed to get choked on not one but two occasions, by completely different people, both of whom I had trusted up until then. One was my friend, and the other was my sibling (who would go on for years to use me as a punching bag. I never fought back. My parents were negligent in both stopping it and getting me any sort of help. I was just expected to handle everything on my own for the most part. Sibling got plenty of care & attention, though, I guess for being the "louder" one with his problems)
Last half of 2014/first half of 15 is also a contender, first year of highschool, completely shut down. Had spent my elementary & middle school years around the same people, and even then I had bad anxiety & barely went. Guess the change just tipped the scales even more.
Honestly hard to place much, time is very hard for me to grasp unless it's a very important detail in a memory.
Last few years have been really bad, too.