Carolyn, I empathize. It is very hard when these things happen. Not only on you; it's hard on them, too.
When the cancer metastasized to my mom's brain, her personality changed so much and her ability to recognize us (dad, my brothers, me) was fleeting in and out, which was difficult enough. But when she started saying things like 'you're a terrible nurse' and things of that sort, it was devastating to hear. My poor dad had to prevent her from jumping out of their vehicle one day when they went for a ride and she tossed her engagement ring out of the window. Obviously he had to stop taking a drive with my mom alone after that. But the memory of that event had to have been horrible for him whenever it popped into his mind. It still bothers me, and I wasn't even there. I mourn not only my mom, but the loss of her cherished engagement ring, which I would love to be able to pass on to my granddaughter someday. (I guess that's my gripe and I know it sounds horrible.)
When my FIL's alzheimer's was progressing, the loss of his mind as he knew it, was devastating to him. He knew it was happening and it really scared him. He was furious with MIL for telling people because he knew it meant he was going to lose his driving privileges, and that's the thing about it that I really can identify with. To lose your privilege to drive when that was your thing has to be one of the great losses. It would be very hard for me to accept, too.
I am so sorry about your wrist. I hope your stepdad's meds do help prevent outbursts, and that you don't get exhausted from the constant vigilance your task requires of you.