You should keep a log of the foods you eat each day. After a few attacks like this, you may be able to find a pattern.
Have you been tested for the Celiac? If you have an intolerance for gluten, a meal high in gluten can cause major discomfort. And it wreaks havoc on your immune system, making one feel drained. Celiacs are also chronically known to be anemic, due to malabsorption of nutrients, exacerbating the 'worn out' feeling.
An initial blood test can be done to check for abnormal levels of endomysial and anti-tissue transglutaminase antibodies. If these levels are high, they'll do a small intestine biopsy.
Anyhow, keep track of what you're eating. You've got nothing to lose, since the docs can't seem to figure it out. Also, it's probably a good idea to get to an ER at the time that the symptoms are happening. Better chance of diagnosis.
