i wouldn't say that i'm tired. my mind is active, even after having worked for most of the day  but focus is hard. despite it being a bad idea for many reasons , i feel like working.
lately it's becoming hard to "shut off" at night.
there are always ideas that come to mind. of course, most of them don't work and some of them are (admittedly) crazy .. but getting a new idea is addictive. moreover, trying them out is like gambling:
one doesn't expect to win anything;
then again, if one does happen to win .. (-:
 woke up at 7:30am, wrote up a final set of lecture notes over breakfast, thought about a random problem or two before heading to my guest office at 9:30, answered some emails and ignored others, met collaborators and discussed ideas and technicalities for projects until the time for lecture, gave a 1-hour lecture, back to collaboration, late Spanish lunch at 14:00, back to work for a few hours ..
 until recently i had been consistently good with not doing maths until going to bed. at some point i developed a kind of mental allergy: now i can't sleep right after thinking about technical details.