Why do I get sleepy when I get full?

I've looked this up before out of curiosity.
Google is your friend.

Anyways:
This happens because when あなた eat all the blood flows right to your stomach in order to digest the 食 あなた have eaten, thus あなた have no will and mood for anything else, あなた just feel lazy and doing nothing. This is why it is healthy to have a rest after heavy meals so that your stomach can do its job properly. It lasts only until あなた have digested the 食 あなた have eaten.

When あなた eat something when あなた are tired, most of the blood will go to digesting the food. So that means almost no blood is going to muscles, and then あなた fall asleep. Also, certain foods determine whether または not あなた fall asleep quicker または slower than usual.

What Heartisalone said. o_o

I KNOW THIS!
I ACTUALLY SERIOUSLY KNOW THIS!

It's because all of your energy and blood flow goes to digestion rather than keeping あなた alert an awake. This is also why some people get really cold after they eat.

What Heartisalone said.

ikr!!!!!:( i do 2 well itz because u stuff your face soooo much and your body ate all dat energy dat u need some rest.......... i think!!!!:)