When you eat that much carb at once, your blood sugar spikes, causing massive insulin production from your pancreas. Yes, it makes you tired.
Mind you, I shouldn't talk. I'm munching on half a pumpkin scone (SO GOOD!) from Cobs bread, because I just walked in the door and I'm exhuasted. Note to self: do not eat when tired. Sleep instead!
It was a very late meeting tonight, and I have another 2 nights of this left this week. *sigh* What doesn't kill you makes you stronger.