I've had this experience with both Ne and Ni where in the case of Ne I can't stop generating new possibilities and alternative viewpoints. This is cool when i'm active, but completely and fucking annoying when i'm trying to sleep. Ni sometimes, albeit a bit less, does the same thing to me, where i'm extrapolating into the past/future replaying events or prognocizing events to the furthest implication possible (usually nothingness) where i desperately want to stop doing that cuz it's driving me crazy.
Alternatively, there's days where Ne is "empty" and is more of a want than a full thing. It prods me to find something engaging but doesn't offer suggestions. This boredom is a pretty annoying state and something i try to avoid, but every now and then I wake up and find that i've nothing that interests me to get me out of bed or into life and i'll be extremely distraught for that day.
Ni "boredom" seems to come about when there's actually nothing to plan, forecast or no-one to figure out. It'll just be there, nagging in the background. Opposed to the idea of "flow" (which I kinda equate to those rare moments when something is interesting enough to captivate me completely) this is a kind of "being in the moment" that's scary in a way, it is as if there'll be no tomorrow and the past seems just something in the now (as a collection of memories). Time compresses to the point where i'm feeling like no movement is possible and everything will stale down to the ultimate end.