The sixth edition of the Publication Manual of the American Psychological Association offers guidelines for style and format in academic writing. Appropriate methods for citing sources such as books, journal articles, Internet resources and personal interviews are included. If a writer wants to reference his own published work, it is cited the same as any other of that type of work. Personal experience is handled differently, as there is no way for the reader to reference the original source.
In the academic world, authors often publish a variety of work on a single topic, examining it from many angles and building upon their previous research. Therefore, it is not unusual for professionals to cite their own published work when developing a new manuscript. Those publications have become part of the wider body of knowledge on the subject, so citations must be made both in-text and on the reference page and follow the proper format for the type of media (e.g., article, book or website). You can also reference an unpublished manuscript if you're drawing from a paper you completed for a different course.
One purpose of referencing work in APA style is to provide details to the readers so they can access the source themselves. If you are referencing personal knowledge, there is no way for readers to find the material and study it themselves. Therefore, personal, unpublished knowledge or experiences are not cited under APA guidelines.