Lets see though...
Physically, it'd be when my tendinitis decided to show itself. My body has a strange way of reacting to pain (and I don't know why), and instead of just localizing to my left elbow, at first I was in full-body please-let-me-die kind of pain. I don't know how much ibuprofen I took to deal with it (I did eventually go to urgent care and the ER, who did nothing), but it was a lot. Enough to make my teeth numb. When it was finally narrowed down and I saw an orthopedic doc, he got me fixed right up with physical therapy and such but yikes. It was so bad. The only other thing that has ever come close to that is the ulceration in my eye from sleeping with contacts in (and almost going blind in that eye) when I was a senior in high school, or the pain of severe tooth decay from a wisdom tooth gone waaaaaaay south. Eye pain and tooth pain are their own special breed of beasts though, for sure.
Emotionally it was losing my mom last year to cancer very suddenly. She had been going downhill for a few years, but it just got rapid all at once from May 2018 until she passed in August 2018 just a week before she was supposed to start treatment. Worse yet was it came only eight months after my aunt, her older sister, passed away from cancer as well. Both lung cancer, but different kinds. Same thing that too their mother (my grandmother), and their aunt (my great aunt). To give you reference (and because I don't mind sharing this), I just turned 30 this year so I lost my mother at 29. She was 59 years old, she would have turned 60 in 2018. It was a really hard year on the whole family. I'm the oldest of three, so I tried to be strong for my siblings, but on top of that I had to be strong for my Dad who was so lost without Mom. He still is.