Couple things because I've delved into this myself a good bit — especially having what I view as a close call doing water-sports at a very warm lake that has a history of deaths from this very thing (cue a week's worth of paranoia....)
Despite it being "always fatal," we don't really know how often it's encountered and that our immune-system is able to get rid of it. (Nobody voluntarily gets it; nobody goes to the ER that isn't sick for the very specific symptoms it presents as).
It has to get very far up your nose and is usually from kicked-up sediment.
Regarding Nasal Irrigation/Neti pot Risk: be sure to use distilled water. Also some bonus information I've written up previously regarding the benefits of nasal irrigation:
If not using it regularly, consider using the nasal-irrigation immediately after being in a "high-risk" environment such as an indoor area with many people tightly packed and at risk of being sick. It will flush your initial viral load and improve your odds of purging the infection before it starts.