Before I switched over to a truly low carb diet, I experienced these "low blood sugar feelings" all the time. I did a good amount of self testing with the glucose monitor trying to figure out what was going on, but never found actual low blood sugar.
Instead I found blood sugar spikes, typically occurring 45 minutes to one hour after a meal. These spikes would approach and sometimes go over 200 mg/dL depending on what I was eating. I always felt fine during the upside of this spike.
The downside was another matter. When my blood sugar drops rapidly, I get all the normal low blood sugar feelings, even if the blood sugar is still technically high. It is the rate of change that seems to bring on the feelings for me.
The video in this post goes a long way towards explaining what was going on for me. One possible symptom of POTS is rapid gastric emptying. Basically my stomach dumps my meal into the small intestine too early and too fast. If the meal contains sugar ( or starches that are quickly converted to sugar ), the small intestine quickly absorbs it, and then I get the blood sugar spike. Reactive hypoglycemia can soon follow, but for me, just the rapid fall of blood sugar was enough to cause problems.