All you need to do for DailyMe is answer the simple and important question "How are you feeling?" You can answer this question as often as you'd like. DailyMe can be found directly on My health to add more context to the other experiences you share there, as well as on your Doctor Visit Sheet so you can communicate more effectively about how treatment changes have impacted the whole you. You can also see trends in how you feel by day of week and time of day.
To add a backdated DailyMe, first add a score for today. Then, on your DailyMe history you can edit the entry to another date. You can even sign up for a reminder and answer DailyMe right over email.