Perhaps you are eating too many carbs or too much sugar at breakfast? I suggest, from experience, making sure you eat some protein for breakfast. If you can I suggest eggs etc. or my personal favorite for weekday going to work mornings--a Zone bar. They are portable and high in protein!
You may be experincing hypoglycemia. If you take insulin you may be taking too much for the amount of food you are eating. As insulin helps the glucose get to the cells and tissue. If you are not taking insulin your body may be releasing a large amount of insulin in response to a meal high in carbohydrates. You need to find a balance as hypoglycemia can cause you to serious problems. I would talk to your dr. right away to find out exactly what is going on but you can not continue to go into hypoglycemic spells because it can be very harmful. Please see dr. asap.
It sounds like gastric dumping syndrome.
http://en.wikipedia.org/wiki/Gastric_dumping_syndrome
It is best treated with changes in diet, as explained in this article.