Does 4getting our past (black history) badly effect our mind?

If someone (clever and always get high marks in their study) who set their mind to forget about few things such as frustration, sadness and sorrows ( want to forget it soooooooo badly ).. suddenly become someone forgetful and not very good in study anymore. I mean their mind become decreasingly noneffective like before. Like Alzheimer's? at about 18 years old and female. Can it really effect?