Yup, that happens to other people with SLE! It probably is from sun & heat exposure...unfortunately the only way to know for sure is to expose yourself again and see if the same horrible thing happens. (I don't recommend this.)
Drink lots of water, stay cool, and I hope you feel better soon!
Lynnwood, Lupus & Sjogren's Moderator, Dx: 2002DIAGNOSING LUPUS & LUPUS RESOURCES
"Life is far too important to be taken seriously." - Oscar Wilde