Just searched MN for 'Febrile Convulsions' as DC2 is prone to them, temperature suddenly rockets...most recent one was Christmas Eve, and almost again on Christmas Night, though just avoided a fit by putting wet (tepid) towel on, then tepid bath before going to hospital. Was alone on Christmas Eve, DH works away, and although due home he was late...he arrived shortly after the ambulance, what a sight to be greeted with 
DC2 had one at 6 months...horrifying, then again at 18 months, one at nursery aged two, one in early hours of Boxing Day LAST year, then on the 24th this year...it's indescribably awful.
The wonderful nurses at local hospital were fantastic, one was the same nurse as last year! Poor woman being on Christmas two years in a row (rural location and I know she has a small DC). THIS year they tested DC2's urine, there was an infection, and reason for high temperature.
I KNOW they do not cause any lasting damage, and that children do grow out of them, but they are terrifying to witness. Calpol, Ibuprofen, and a good thermometer are essential. If in any doubt go to the Hospital.
I hope your little boy feels better soon. xXx