If the body temperature gets cold and hot is that a symptom of sporadic fatal insomnia?

Fatal insomnia: Yes. Fever is one of the symptoms.

These are irrelevant: For diagnosis of this disorder. If you are pre-occupied with this diagnosis, the more relevant question is why? What psychological benefit does a possible diagnosis of fatal insomnia give to you? Some patients secretly wish that they have a rare disorder so that they can attract attention and become special or famous. Even when provided evidence to the contrary, they have a hard time accepting.