Functioning better when lower?

So it’s finals season and I usually start studying around 1 or 2 each day (yeah, I know, great life). Some days I have lunch, some days I don’t. Interestingly enough, when I don’t eat (or have a handful of nuts or something), I find that my BG is in the high 60s or 70s and feel great, focused, and high-energy. When I eat carbs and bolus, it’s in the 100s and I feel tired and groggy. Is this something I should worry about? Obviously I don’t want to be any lower than about 70, but with no bolus insulin on board and a bag of glucose tabs and candy in my backpack if I need them, should I worry about being that low if I feel and function better?

It is an issue I deal with too. I feel great in the 70’s. Over 100 I feel tierd. The bad part is at 70 if you doing any activites it could drop quickly and lead to you going out. Not sure why I that is that at 70 I have tons of energy, my moods are fine and I am able to get more programming done.