I'm glad your little guy is doing better now! My ds was just diagnosed today. Spent some time at the Children's Hospital but fortunately we were able to come home. They have seen quite a bit of this recently. We had 2 other cases at our school, one of which the child spent 2 weeks at the hospital.
My ds has had a fever but no other symptoms. Then this morning when he woke up, he complained of pains in the back of his legs and was unable to stand - and has been walking on tiptoe all day. The doctor gave a preliminary diagnosis of viral myositis, which was confirmed by a blood test. If I understand correctly, Viral myosistis is a muscular inflammation brought on by a flu-like virus. There is potential concern for kidney problems, which is why they want you to drink alot of water. Flush out the bad stuff.
This is a virus that I'd never heard of before. If your child develops similar symptoms, call the doctor so they can tell you what to watch for.
{{{HUGS}}} to all the sick little ones!