I have seen it written that it is especially very important for narcoleptics to keep properly hydrated because for some reason they "forget" to drink when they are dehydrated. Here is an interesting tidbit of neurology that at may least in part explain why. Please note that the conclusion I am drawing here has been tentatively validated by one person who works in the field, but is otherwise only speculation on my part.

When you are dehydrated your brain releases the excitatory neuropeptide vasopressin which is an antidiuretic. Dynorphin, an inhibitory neuropeptide, is co-localized on vasopressin neurons and its expression is increased during dehydration episodes. The dynorphin inhibits the release of vasopressin even as the neuron receives electrical impulses telling it to release more. The dynorphin also acts to reduce the release of the excitatory amino acid glutamate from presynaptic vasopressin axons. This two pronged inhibitory action of dynorphin MODULATES the release of vasopressin so that it is not over-released, and you'll become thirsty.

Now, dynorphin is also expressed on orexin neurons. So if the orexin neurons are absent or crippled in some way (narcolepsy) and can't contribute dynorphin during a dehydration episode, too much vasopressin is released, you won't be as thirsty, and you'll "forget" to drink.

You’ll also possibly wind up with high blood pressure, as one of the the ways vasopressin keeps water in the body is by increasing blood pressure through vascular contraction.

If you can validate or debunk this, PLEASE do.