Memory loss (amnesia) is unusual forgetfulness. You may not be able to remember new events, recall one or more memories of the past, or both. The memory loss may be for a short time and then resolve (transient). Or it may not go away, and, depending on the cause, it can get worse over time. Normal aging can cause some forgetfulness. It is normal to have some trouble learning new material or needing more time to remember it. But normal aging does not lead to dramatic memory loss. Such memory loss is due to other diseases. Memory loss can be caused by many things.
Click here for more information: http://www.nlm.nih.gov/medlineplus/ency/article/003257.htm