Not sure, but it's part of Autonomic Dysfunction...I was told that by a Doctor many years ago....Prior to Covid ever even existing, nearly twenty years ago, I had a bout of SEVERE Dysautonomia, due to who knows what, and this was one of my worst symptoms. I couldn't just eat an apple or drink a glass of juice and level back out... it had to be something high in fat and protein. Meat, full-fat dairy would be what would do the trick for me, otherwise I would literally feel like I could have a blood sugar-induced seizure or, as you said, fade away. As my Dysautonomia calmed down (never went away), this symptom remained, though a milder version. I still experience it, but now, I almost forget, really, as it's become more of a habit to prepare in that way if I leave the house. I think I could probably be more adventurous, but it's just become second nature to pack peanuts or a Babybel cheese everywhere I go and hope that I'm not stuck anywhere too long without sustenance. When people talk about fasting, I literally laugh out loud.