It could be more than just a bad day.
The most important way of getting proper treatment is to give the doctor as much information as possible, so tracking moods is an invaluable method of gathering that information. Below is a link to download a printable mood tracker which can be folded to the size of a credit card.
The tracker records the general mood of the day, from depression to "elevated" mood (a more easy to recognize term for "mania"). It is also important to note anxiety and irritability, as well as whether women users are menstruating or not. Be sure to fill in medication information as well.