Like everyone else says -- you need to get a medical opinion.
My first guess was that it was anxiety, but from what I gather and in my own experience, anxiety attacks occur randomly. The regularity suggests something metabolic, I would think.
BTW ~ M&M's would work in either a sugar case or an anxiety one. The sugar thing is obvious, but chocolate also contains the chemical dopamine to make you feel good. The best hit of this comes from bittersweet dark chocolate, if you want to experiment. It's my drug of choice.