Hi Lupus fighter,
Actually, what you experienced isn't weird. It's completely normal for those of us with lupus to have a very difficult time with the sun. It's great that you're using sunscreen, but it isn't enough. You need to keep covered up, and in the shade. If you routinely spend time in the sun, you WILL end up in a flare. Lupus and the sun, or heat for that matter don't mix at all.
So you didn't experience anything strange. You experienced exactly what lupus and sun do together. They clash!
Stay in the shade!
Ginny
Also, prednisone makes our skin very sensitive to the sun. So a sunscreen with SPF 30 is the minimum we should be wearing. 45 or higher is better, and apply it often even when you're not sweating or in the water.