Why does a gluten free diet help reduce narcolepsy and cataplexy symptoms for some narcoleptics even if tests show they have no gluten sensitivities?

It probably doesn't.: I don't believe that a gluten-free diet would treat narcolepsy. A thorough search on pubmed did not reveal any publications demonstrating a connection between narcolepsy or cataplexy and gluten consumption. It is possible that by adopting a gluten-free diet, one might also consume fewer simple carbohydrates, and that could reduce reactive hypoglycemia (which can make you feel tired).

Not entirely known: There is a link between carbohydrates and narcolepsy. So similar products containing gluten and carbohydrates and just the digestion of gluten itself may contribute. It is one of the things that i talk to my newly diagnosed narcoleptics about.

Gluten sensitivity: Many people have sensitivities to gluten even if they don't have celiac disease. Some symptoms can be fatigue, sleepiness, difficulty concentrating, and "fuzzy thinking" -- which can all overlap with narcolepsy (at least the falling asleep part). If you are a person with this food sensitivity, you could feel a lot better off gluten -- even though this does not cure narcolepsy.