What Does Lack Of Response After Concussion Indicate?

My daughter (14) had a concussion a few months ago. Since then she has these moments when she stares into space and becomes unresponsive. She says everything goes black. She can t hear anything. She can feel if someone touches her but can t respond. The worst one she had lasted for 3 minutes and her pupils dilated until you couldn t tell what color her eyes were. She has had a severe headache since then ( about a week) and feels like her head is bleeding even though it s not. I took her to the ER and CT and EKG are normal. Any idea of what might be going one. I feel so helpless