http://www.ncbi.nlm.nih.gov/pubmed/18779282) concluded that "cognitive performance, activity, sleep, and mood are not adversely affected in healthy humans by 2 [days] of calorie-deprivation. Granted this is only one study (I haven't searched for more), but it seems relatively clear that the numerous mechanisms for raising blood glucose concentrations (http://en.wikipedia.org/wiki/Blood_sugar_regulation) combined with a normally functioning pancreas and insulin regulation would be able to maintain a functional state without totally throwing you for a loop regarding cognition.
On an additional note, a second study (http://www.ncbi.nlm.nih.gov/pubmed/2405701) concluded that the decline of plasma glucose (as a result of fasting) clearly contributes to an increase in lipolysis; but again, that's a just a positive tangent!
But again, everything affects everyone slightly differently! Personally, I would look to confirm any issues regarding the up-regulating mechanisms to make sure there are no underlying problems first. Whether the science is there or not though, I have come across individuals who feel woozy if they go long periods without food; MB suggested the transition to utilizing ketones as opposed to glucose may result in temporary disorientation. However, I'm not totally convinced any such conditions are strictly due to inappropriately controlled blood glucose concentrations as opposed to one or more other physiological factors.