This has happened to Grace, alot for many different reasons.  First, if she gets overheated she gets sick for at least that day (sometimes the next day too.)  Secondly if she is just playing too hard one day, she will sleep alot the next day.  Thirdly, when she had her last "brown out (as Dr.Cohen called it)" her sleeping patterns were off for about two months. This was brought on by a virus we didn't even know she had.  It started mostly as sleeping alot and she was very clumbsy, eventually it caused alot of other problems (most of wich resolved themselves with time.)  I would call the mito doc. if it goes on for too much longer.  Better to be safe.  Best wishes, I will pray he is full of energy really soon.

Carrie