Recall

Lately, I hardly recall the material that i had read and saw about its. It's occur recently, especially during my examination my memory can totally wipe out. My results is decline as i had fail some paper. I'm not sure what happen and why it can be happen on me. Some said it happen cause the brain didn't get rest well and lack of vitamins affected brain work efficiency. Is this a disease or normal? Do others have this problem as i had? Can it be treat? Many question on my mind now as i worried it can't be treated if the time missed.