Private feelings and personal experiences are expressed frequently in a daily writing called a

Diary / journal / notebook. 
A diary (sometimes referred to as journal or notebook) is a record (originally in handwritten format) with discrete entries arranged by date reporting on what has happened over the course of a day or other period. A personal diary may include a person's experiences, and/or thoughts or feelings, including comment on current events outside the writer's direct experience. Someone who keeps a diary is known as a diarist