at night, the amount of light that enters your eyes are reduced
and it stimulates your pineal gland to secrete melatonin. melatonin
induces sleep, and also causes your amygdala to retrieve emotional
memories. that is why people usually feel their moods dampen in the
night.
so much for that useless fact. 
just go and sleep lah. close your eyes, listen to music.... relax
and soon, you will be zzzzzzzz ing.
