I would have to disagree with this. It would be a very abnormal response for blood sugar to go so low that cortisol has to kick in to activate gluconeogenesis. Glucagon kicks in way before it gets to that level. You would know, because severe hypoglycemia would occur (anxiety, palpitations, hunger, sweating, irritability, tremor; or in more extreme cases, dizziness, tingling, blurred vision, difficulty in thinking, and faintness). I wrote an article about this here: Ketogenic Diets, Cortisol, and Stress: Part I — Gluconeogenesis.
The article is about fed ketosis, and I concede that there is a higher likelihood of it happening during fasting. In fact, it's been reported sometimes in children who are fasted in preparation for ketogenic therapy for epilepsy. Again, though, if this is happening to you, you'll know. It won't be a silent side-effect.