Our body produces melatonin - the substance that makes you sleep - depending on the amount of light received by our eyes, and possibly also our skin. So it is natural to sleep when it is dark outside.
If you live in a city with street-lights or other artificial light sources in the night, unless you have good light isolation on your windows, those might be disrupting your body's melatonin production and thus your natural "sleepiness" cycle. I have also read that CFL's (mercury fluorescent tubes) and LED (diodes) light sources are especially "effective" (=bad) in this disruption - because they emit disproportionately high amounts of low-frequency - "blue" - light.
When one has disrupted melatonin production cycle, one might tend to get sleepy in a different pattern than the natural one, based on sunlight.
HOWEVER, I think it is also normal to become tired after eating a big enough meal - digestion of food takes energy. If you eat during the day, you might have a tendency to sleep because of that.
And people are living organisms ; not ("wired") machines.
