there are several factors for me that can cause me to forget things...stress, anxiety, depression, dehydration, not eating or sleeping enough, etc. sometimes it can be dissociation for me, but i can generally figure out what the cause is if i pay attention to how i am feeling around the time i notice it. sometimes medication can also cause a person to forget things due to side effects. so, there are any number of things that could be a reason for it.