What Could Cause Sudden On And Off Loss Of Memory When Focussing?

Hi, I have a problem and i'm not sure what it is. A few years ago when i was about 10 years old, i woke up out of my bed and i never remembered anything before then. I remember sometimes but not that much. I have never been hit in my head before, i don't have steady headaches or anything of that sort. I am always focused and a quick learner but i am not sure what the problem is or what causes this sometimes. At times i would sit around and gaze or take hours to remember what i am looking for. But strangely this only happens sometimes when i'm focused. Thank you for your time, please advice?