Is reanimation of dead people by extraterrestrial spirits a widespread phenomenon?

That is not the case, with the exception of some Reptilian mischief where they may dispose of a human and send an imposter in their place, as you currently are aware. The Annunaki do not do this, nor do any of the spirits reanimate a deceased physical body. There is no need to do this. The extraterrestrial Reptilians can replace them seamlessly as imposters, and that way the subterfuge is complete. The extraterrestrials can commandeer living humans and control them from within. That is a different matter. And so there is a phenomenon of subjugation to make people march to their tune by controlling them quite powerfully at times and overriding their own conscious choices. That is done through the living, not the deceased.