My niece suffered from febrile fevers. We lost her during a seizure spike in a bathtub.
As I am now naturally hyper sensitive, I spoke to a Children's Hospital Nurse and armed myself with info. In general: If the child is past two with no previous history, it is unlikely they will suffer a febrile seizure. The markers for the seizure isn't that the temperature gets so high, but rather how fast it spikes. A fever in general is a good thing as it is the body's way of 'cooking' the bad bugs.
Hope this helps. That said, anytime my daughter gets a fever I get nervous. I can't imagine how a caregiver feels.
TorontoKids, you did great! If you are ever REALLY scared, call for an ambulance. As a parent, I would rather the safe than sorry.