Do i have some sort of Glucose Imbalance?

I try to eat really healthy however I become very tired and depressed over the last year or so. However, it seems whenever I eat a chocolate bar I feel full of energy, I can focus, I feel happie, and this is over a sustained period of time (its not like a sugar high). If i go on eating healthy food and eliminating sweets i get all depressed again I can not focus I am agitated so I am thinking I have some sort of blood sugar imbalance. I don't know anyone have any thoughts. Also, I am one of those people who can eat as much of anything I want and not gain a pound.