Toss up between tearing my ACL in October 2009 or herniating a disc in my lower back sometime early last Summer (2014)
Torn ACL happened right after school. We always rode our bikes to school and when we got out that day it was starting to rain a little so the roads were wet, I did a bunnyhop x-up off a curb cut going fairly fast... No problems there. But then I tried gapping from a line in the road to another line, probably like 5 or 6 feet long so I hopped as high as I could but my feet slipped off the pedals and I was going to just land on my feet but I guess since the road was wet, my right foot slipped and bent my knee 90° & slammed the ground like that too... Adrenaline was rushing so I somehow managed to get back to my bike & ride off, then the pain set in so I had to get picked up and taken to the hospital. They did like 1 x-ray and didn't even consider the possibility that something could be torn, and told me I should be good by Monday (It was currently Friday) well come Monday I'm still in pain and can barely walk, got scheduled for an MRI and confirmed it but since I'm a dumbass I didn't get surgery yet cause I didn't think I absolutely needed it cause a dipshit doctor mislead me into thinking it could be strengthened and supported with a brace and surgery wasn't a priority really... Well, a month later I was trying a manual to feeble 180 line and the one time I did the 180 out I planted my leg weird and it popped again, felt like I tore it all over again. It fucking hurt so bad I could hear and feel the bone grinding as I fell to the ground. Finally scheduled surgery, early December at a different hospital who did a great job, did rehab for it and all that good stuff, anddd nowadays I'm perfectly fine, minus the scar on my leg that is still really tender. Hurts like hell if I hit it. Also pretty cautious if I ever have to plant my right leg for anything out of habit.
Back problem happened starting sometime in June 2014... Not sure exactly what did it for sure, could be a number of things but I still have no 100% confirmed reason why it happened. I'm dumb and let it get bad to the point where I couldn't even walk or lay down without pain. Got small dosage steroids for it which helped a lot and allowed me to ride again for about a week when it all went downhill again. Got an MRI, confirmed it was a disc herniation, and got a steroid injection shot right into the nerve. Calmed it down almost instantly but I still had a while to go before I was able to ride again. Took about 2 weeks, but I was then able to cruise around with very little pain, and as the weeks went on I slowly eased back into it with minimal pain. At this point I wasn't stretching or doing any core strengthening exercises, so after awhile it started hurting like hell again. I was maybe back to 60% of my riding skill at the time. Got another shot for it which did the trick, went for like 2 months without pain then it started up again and the doctor prescribed me those low dosage steroids again and told me I should be stretching and strengthening my core (He told me that before, but I honestly didn't think it would do much to stretch my hamstrings.. Boy was I wrong, that shit worked wonders!) so I took the steroids, did stretching and strengthening, and I do that every other night now and I can ride all day without feeling it now.
That's not to say it isn't there anymore, it never fully heals or goes away but it is definitely manageable. I feel it more when I'm not riding actually haha