Zombie, I'm sorry to hear about your uncle and your struggles.
I had a situation that changed driving for me. Oddly enough, driving does not usually cause anxiety for me. Actually it was always a safe place for me to be, and I found it enjoyable (as long as I know the area).
I was driving my regular route with my daughter in the car. I stopped because the car in front of me stopped to turn. A young teenager rear-ended me. I slammed into the car in front of me and did a lot of damage to their van. Here I was, minding my own business, and a situation beyond my control changed the course of my day-police, insurance, paperwork, etc... I was shaken up.
I felt so paranoid to drive for a while after that. I kept checking in my rearview mirror to make sure people were not driving too closely behind me. I was always gripping the steering wheel. I was so anxious I felt I could just cry whenever I had to drive. I was mad that something I HAVE to do now was causing so much anxiety, on top of all the other things I worry about.
I started to try to find a positive. I can't control what other drivers do, but I will always make sure to drive the speed limit. Before, I may not have been so vigilant. Maybe I drove a little too closely to cars in front of me. I used the experience as a way of improving my skills.
Over time, my fear lessened. Now, I'm back to feeling comfortable. I know my situation is different. Losing a family member in a serious accident is horrific and certainly has more lasting effects. As you said, your uncle may have had a health issue that caused the accident, so his driving didn't play a direct role.
Keep driving; it will get better, but get help if you need it.