Amnesia
Amnesia is a deficit in memory caused by brain damage or brain diseases, but it can also be temporarily caused by the use of various sedative and hypnotic drugs. The memory can be either wholly or partially lost due to the extent of damage that is caused. There are two main types of amnesia: Retrograde amnesia is the inability to remember information that was acquired before a particular date, usually the date of an accident or operation. In some cases, the memory loss can extend back decades, while in other cases, people may lose only a few months of memory.