Is there any clearly identifiable reason explaining why sleeping during the day (for longer than 30 minutes) could produce lowered mood, difficulty in concentrating, overall decreased cognitive performance etc., with symptoms persisting during the rest of the day? This might be somewhat related to sleep inertia (http://en.wikipedia.org/wiki/Sleep_inertia), but persistence of symptoms for many hours might prompt for a different explanation.
Effect of mid-day sleep on mood and performance
sleep