Why am I feeling flighty?

Sometimes when I eat healthy and within my caloric goals I feel flighty. Like I cant concentrate, I am forgetful and I don't feel well. Do I need more protein or carbs?? What am I missing? For Example: This morning I ran 2 miles, I then came home and had a bowl of bran cereal 3/4 c. with a cup of milk and a banana (around 8am). About 10am I was feeling super flighty. I couldn't focus and everything seemed confusing (work wise). I decided to eat a string cheese and about 6 pieces of turkey pepperoni for a snack, thinking maybe I needed protein. But, I didn't feel better. I then went and bought some almonds thinking maybe it wasn't a protein problem and maybe I needed more food since I had only ate about 400 calories and had exercised 175. I ate about 12 almonds and didn't feel better. I don't know what I am missing. Does anyone have any suggestions? Do you ever get like this?