This happens to me when I really dive into something. It
happened when I first started learning Perl and still
happens when there is a challenging (read: difficult to
impossible) project on my plate.
It's not necessarily a bad thing, though... I have often
woken up in the middle of the night with a solution that I
just have to start working on before I forget it.
ummmm........ maybe it is a bad thing, after all...