Scombroid Food Poisoning
Unless you live on the coast and get your sushi fish straight out of the ocean, you run the risk of getting scombroid food poisoning. Never heard of it? Roughly 38% of seafood related food poisoning outbreaks are scombroid food poisonings.
If the fish is not kept cold enough during transport, it begins to rot. As the muscle begins to break down, it releases a histamine. You get an allergic type reaction including flushing, rash, headache, dizziness, and sweating. A severe enough reaction can cause anaphylaxis.