Fever vomiting headache. Thing serious?

Today, all of a sudden my son got fever with headache which started with 100° and kept rising till he took Calpol 250. He was complaining of headache near his nose. I wasn't able to understand exactly what he wanted to say but he was saying his legs and other body parts are getting hard.  I thought it might be dry so have plenty of water to drink.He was having sprouts which he vomited in projectile motion. When the fever was raising,his eyes n face looked very sick. I gave Calpol 250 5ml and took him to the doctor. He did analysis and prescribed Calpol 250, Mefanorm, Aziclass. While coming back from the doctor, his fever reduced due to Calpol, he became all activity. He played normally and ate m slept. Is there any thing serious ? We are really worried. Please help.