Discrimination or not?

This may be a long post but I think it's necessary to have background information.
I was diagnosed with epilepsy about 2 years ago and it has never affected my work. Recently, I had a checkup which included a 72 hour EEG. The results showed that I was having seizure activity at least once an hour. My doctor urged me to limit my stress. At my job I work at the highest level of management. After careful thought and family discussion I decided that for my health I needed to be in a less stressful environment. I spoke with my boss and told him that I was having an issue and needed to be placed in a less stressful location. Unfortunately, the only locations available were lower level management positions. He said there were no other options and that I could take the lower level if I wanted but to him it was clear that I couldn't perform my job. Now it is important to say that in the past year I have had the highest employee rating every rating period. I felt like I had no choice but to take the lower level or id be managed very closely.
After agreeing to move to a lower level my boss informed me that I would have to take a 10% pay cut because my salary was above the maximum for the new position (the lower level). Now I understand that. In the past week I have personally talked to 2 people that were demoted from the level I was at to the new level for lack of performance and they flat out told me they did not receive a decrease in pay. I couldn't believe it but they actually showed me pay stubs.
I also spoke with a regional who I know closely and is a family friend. She informed me that this is not the normal course of action and when someone gets demoted even for performance reasons that they don't reduce their pay.

So now I'm stuck. I should also mention that a month ago my company went on a campaign asking people to declare themselves for equal opportunity and a diverse employee population. People could declare themselves as disabled and I did so.

Is it discrimination that I had to take a 10% pay cut for taking the lower level management position while other who made the same exact move due to underperformance were able to keep their salary? Something just doesn't seem right to me. I did not ask for this disability and have performed well in spite of it.