Sleep journal, sleep window, sleep rhythm

• Why can a new entry to my sleep journal not be saved?
• What does the field "For how long was your sleep interrupted" mean?
• What's the difference between performance, energy level and mood?
• What is the definition of sleep quality and sleep efficiency?
• What's the purpose of the sleep window?
• How can I motivate to stick to the bed time reduction?
• What to keep in mind when starting the bed time restriction.