Tired and confused after sitting

Hi all

I am a reactive hypoglycemia sufferer since i was ten.

I am a student; in this period, when I sit down in the afternoon to study, after one hour or so I feel tired and confused. It is not exactly like a classic hypoglycemia attack, since studying while standing up (I mean, not sitting down) allow me to avoid that umpleasant feeling. Have you ever experienced anything like this? Have you ever read or listened about similar cases?

Moreover, what is your typical diet?

Here is mine:
no breackfast;
lunch: tuna, green salad, a little bit of whole bread
no afternoon snack;
dinner: same as lunch.

Whatever I eat on breackfast,even protein or fat, just stick into my stomach and make me drowsy and tired.
Often, before going to bed, I take another little dinner, with salad.
So far, this is the diet that worked best. Also, I take a vitamin/minerals supplement on regular basis.

Thank you for your help