Naegleria fowleri

Naegleria fowleri is a brain-eating amoeba which is found in warm bodies of water. If it gets up your nose or otherwise finds its way into your brain you are dead. Less than 1% of the people with naegleriasis survive. You'll have a high fever, hallucinations, and intense pain which painkillers won't work on (as the pain is coming from inside your brain), fall into a coma and die within 5-7 days of exposure.