What Causes Severe Heat In The Legs Followed By Swelling?

I went to the mall yesterday and walked a lot. Right before I was ready to leave, I noticed that the bottomes of my legs above my ankles on both legs were burning and really hot. I sat down and pulled my pant legs up and seen that they were blood red and swollen and felt like they were going to catch fire. What could this be? They are still like this and I slept with my legs elevated last night as well.