All prion diseases are kind of similar, but no, I don't think FFI is the worst of them. The defining feature of FFI is rapid dementia and then death, not necessarily insomnia.
I think Mad Cow Disease (new variant Creutzfeldt-Jakob Disease) is the worst of them.
* Protracted course 1+ year from onset to death. Maybe 1.5 years is not unheard of.
* Almost purely psychiatric issues at the start, not even cognitive.
* But it ends in akinetic mutism, which is when you want to move, but a counterwill energes preventing you from moving, and you want to speak, but a counterwill prevents you from speaking. Locked-in syndrome.
