exercise and hypoglycemia

I've been having disturbing symptoms during/after exercise.   I do 30 mins of cardio every day or every other day...I don't bother with resistance training...can't with my back pain....My routine is to target my heart rate 145-150 and up to 162 during the middle 10 minutes.   Lately, I have noticed towards the end of my workout, during the cool down, the last 10 minutes,  I begin to feel lightheaded...I get the strobelight effect in the middle of my vision, and my entire field of vision begins to darken somewhat.   At first, I thought this is near syncope, but recently I had a severe occurrence which my instinct told me to take my blood sugar, so I do and it was 39.  I was on the verge of collapse and quickly drank a 12 oz soda and some orange juice.  My sugar then shot up to 145 and although shakey (shaky) I felt a lot better.    30 more minutes rolled around, I ate rice and chicken, and in the middle of my meal I began feeling lightheaded again...sugar had dropped back to 52, so I drank another soda.   Glucose doesn't stay high too long with me, 20-30 minutes after a big meal it's back down to 80   Earlier this year I was checked for diabetes, along with other routine blood tests.  I've also had an echocardiogram for palpitations and and brain MRI for headaches/lightheadedness.      And yes, I do eat before I workout.   Do you know what's wrong with me?   Do I need some kind of major workup? I am 30 yrs old.

[Cleveland Clinic]

You may have a very rare tumor in the pancreas which produces glucagon and causes hypoglycemia. This is not a cardiac problem, and you should ask you physician to work you up for a glucagonoma.

[ohsnap911]

PS-  Even after my sugar stabilizes, I still feel kind of bizarre for a long time after this sort of incident.   Is it likely that there is also some other blood chemical out of balance as well?