Sounds like a pretty textbook case of schizophrenia or multi-personality
Cyndy would be the other self of you, and it sounds like shes a pretty rational type of person.....
Maybe you should look up some information about schizophrenia
http://en.wikipedia.org/wiki/Schizophrenia
Its pretty hard reading but it could give you an insight into what the letters are about and the time periods that are missing from your memory
Hope this helps
Devia x