My worst injury was 3 years ago.
I badly sprained my right ankle while dismounting gracely. There was a slope on the sidewalk I was on, where I put my foot, and I didn’t pay attention.
I heard an audible “crack” sound in my ankle. 
I was pissed off because it was just a day before I was supposed to do my very first trail ride with other unicyclists near Paris, and I couldn’t attend it.
I started physical therapy quickly after the injury, I couldn’t ride for three months and the pain lasted for more than six months.
Now, I’m always extra careful when I dismount from my unicycle.