Hello, Lillyleaf! I don't have answers to your questions, but I do know the frustration of moods that have no apparent cause.
Do you remember what was going on in and around you before you slipped into that very low mood? Tell those who are caring for you about your experience. The more information you can recall and offer, the better your chances of answering those questions.
If it be possible, may you never sink so deeply again.
__________________
My dog

mastered the "fetch" command. He would communicate he wanted something, and I would fetch it.