Poor memory lately may be caused by excessive mental stress, stress or irregularity in life or excessive late nights. It may also occur if one is in the pre-Alzheimer’s stage. Alzheimer’s disease is a degenerative disease of the nervous system, the exact cause of which is still unclear. Patients in the early stage mainly show recent memory loss, and can appear to be unable to remember what has just happened, or what has just been said, and often forget phone numbers, turn off the gas, or the names of familiar people. Patients may experience hallucinations, delusions, not recognizing their spouse, not recognizing their old friends, thinking that visitors are burglars, being frightened by the image in the mirror, etc., which may eventually lead to loss of personality.