Memory loss

My 25 year old daughter occasionally has episodes of tempory memory loss. She cannot remember events that have occurred in time frames of a few previous hours or a whole day. She can't remember what she was doing or where she was. Also, as she tries to remember, she will slip backward and realize that she has forgotten what she has just remembered. She will ask the same questions over and over and then suddenly say that she just felt the memories leave her and say in frustration "that was all a waste of time because I have forgotten again". Then she will start asking the same questions as she already asked. This morning the pattern repeated itself many times. She gets very upset and frustrated and overwhelmed with memory loss. Has anyone encountered this type of problem before?