Aye! Sun Seeker, I know what your going through, when I get my " dark spells" (that's what I call them) I get very tired, but at the same time I can't sleep!
I feel totally exhausted, can't concentrate on anything, I feel restless, it's a horrible feeling to have.
I often feel totally worthless, and have no self esteem, in fact, it makes life unbearable?
That's why I always try and make the best of the good times, when I dont have a dark spell