If your child goes into heat stressed convulsions(induced by high fever) put him into a cool bath. If that doesn't help, call the paramedics. Be honest about any meds being given. You don't need anything fancy, just a cool bath, and hold the child until his convulsions are thru.
I also suggest you give him plenty of liquids, especially water. You can make a thin banana smoothie with water, ice, and banana.