Yes!!! That happens to me a LOT! It's happening now, actually. I'm not depressed the majority of the time, but I will have VIOLENT mood swings. Yesterday, I felt fine. This morning I woke up and I was so low that except for the one hour I managed to drag myself to class, I have spent the rest of my day in bed. I make doctor's and counselling appointments all the time but if I'm not feeling low on the actual day of the appointment, I have a hard time convincing myself that it's necessary.

What I do is try to write down how I'm feeling when the lowness hits, and record the date so that I have proof, when I'm feeling better, that the low feelings really did happen, that I really was having a low spell and that I really was concerned by how low I was for no reason at all.

It won't hurt for you to make an appointment with your gp. Tell him/her that you've been having these mood swings, and get a proper physical to rule out any physical causes for the sudden shifts in mood. Just tell your doctor what you've put here, maybe even bring your post along if you think you'll have a hard time explaining it. It's really hard to put this condition into words when we're not currently in the grip of it, but that doesn't invalidate the way you're feeling when you are depressed.