My worst fear is getting some form of dementia. I think I can handle losing limbs or other serious injuries, but losing my ability to solve problems or communicate would be terrible. The reason I became a software developer was because I enjoy solving problems and my ability to do so is a major way that I define myself.
The professor of the usability class that I recently started was diagnosed with Parkinson's disease. Parkinson's disease primarily affects the motor skills of an individual. However there are also symptoms that effect the brain, including dementia and short-term memory loss. There is currently no cure for Parkinson's disease. Michael J. Fox suffers from Parkinson's disease.
Although I am sure the professor is brilliant, he was unable to communicate very effectively due to this disease. One of the symptoms is hypophonia or soft speech. The room was deathly silent for 4 hours during the lecture, any noise (such as changing position in a chair) was a distraction.
Another symptom that I noticed was short term memory loss. The professor frequently paused during the lecture, often times in the middle of a sentence, trying to remember what he was talking about. He also went off subject often. Normally this wouldn't bother me, but I was having a hard time paying attention already and I didn't really know what the course was about, so I was often confused about what he was talking about and whether it was part of the course, or something else.
For a class called Visual Media in Technical Communication, I found it a bit ironic that there was no visual presentation for the class. Perhaps before the professor contracted Parkinson's disease he wrote on the white board or something, however, he sat while he did the lecture (I've never had a professor sit while they did a lecture). Of course, symptoms involving motor skills are the most common symptoms of Parkinson's disease and is probably the reason he sat through it.
As you can probably imagine, I dropped the class. I feel guilty about dropping the class. It's not the professors fault that he wasn't able to perform his job very well and I'm sure he isn't ready to leave a job that he's been doing for many years. Considering that this is my greatest fear, I am certainly sympathetic to his condition.
If you are interested in learning more about Parkinson's disease, there are a number of organizations out there. The following list is from the Wikipedia article...