MMR and high fever

Hi parents, my son had his one year old vaccination - MMR on Tuesday. The nurse said that fever will come one week later but he suddenly developed a fever after his afternoon nap today (Thursday). I gave him ibuprofen earlier at 3pm since his fever was 38.8. His fever suddenly spiked to 39.4 and he was almost unconscious. I was so panicked. We gave him cold towel sponges and managed to bring it down to 38.6 now. KKH said that I should bring him down when his temperature is 41 and above. I’m just wondering whether there’s anyone with similar situation. I am monitoring his temperature very closely. This is so worrying.