Experiencing great fatigue is not much of a surprise when you suffer from bipolar disorder. After all you have been spending a lot of energy bumping around inanely when you were in the manic phase of the syndrome. And now that you feel down in the dumps, also pointlessly I might add, you have begun to feel the characteristic lack of energy.
Well, that's how it is with the mental disarray, and it is going to happen again, and again, constantly getting worse, until you get yourself some medical attention.
You know that feeling of being worn out like you have been carrying a heavy burden? Of course, that very feeling. That's bipolar disorder for you. You probably don't even know why you are feeling so down, particularly since you were practically ecstatic only yesterday. No surprises there either. Manic-depressive people never know why it happens to them, it just does. And the only way to get rid of it is through the right medication... and that under supervision.
It is probably no news that depressed people often have difficulty thinking, culminating in poor concentration and problems with memory. What might shock you is if you saw them outside picking a fight for no apparent reason when only minutes ago they could not even get off of the bed because 'the sky was going to fall down on us all!' Yeah sure, that happens too, when the depression has pushed the sufferer to bipolar disorder. So, rather than drop your jaw, drop your handbag, and get your friend some serious help seriously.