I do feel like that a lot, but you're right, it's good to be able to know why you feel that way instead of worrying if you're going right back down. Even simply recognising that can help your mood not to get any lower. Try doing things you enjoy and eat lots of chocolate
I agree with Crazy Rabbit Lady, if you are finding it really difficult to deal with then try talking to your doctor. If you are embarrassed then maybe you could phone them or write a letter. Hope you're ok. Take care. xxx