Every month I fast for 24 hours. This has never been a problem for me up until the past two years. I noticed that I would often start feeling light-headed and very tired, but it never seemed a major inconvenience.

The past 8 times though, it has been really severe. Anywhere between 12 and 16 hours after my last meal I will get extremely lightheaded. In three instances, my entire vision has gone black (I didn't lose consciousness however) or I'll get what feels like tunnel vision where I can see what's in the center of my vision, but everything else looks either dark or really weird (like someone's shining a black light on it). Also, my face and hands feel cold.

Also, and even scarier to me, in one of the three really severe incidences, I'm told (I was busy trying to deal with black vision and really feeling confused and not thinking clearly) that my entire face turned white and my lips turned blue.
At the time, my face felt cold on the outside, but really hot and flushed below the surface.

I suspect hypoglycemia because in all of these light-headed instances, eating something has relieved symptoms within half an hour.

It's getting worse though. I've noticed that if I skip just one meal now I can feel myself starting to get light-headed, especially if I'm physically active. Plus the onset of light-headedness is sooner after I last ate.

Is it probably hypoglycemia? Do I just need to pack food with me, or should I be worried about some underlying problem? Should I see a doctor?

PS-I am not diabetic (so it's not a diabetes medication problem)