Somehow Picard (and I say this with the kindest intentions) I get the impression you already know the answer to your question.... and have always known it.
The body works hard at digesting food, especially when we eat a large meal. This "hard work" digestive process robs blood flow (and hence oxygen) from our brains, because the body is dedicating resources elsewhere (to the digestive organs). Your brain says "I'm tired".
By the same token, your body will feel the cold more after eating. Once again, instead of circulating blood flow where it's needed to keep you warm, it's working on digesting that meal you just ate.
As my fellow compatriot President Bush might say "It's hard work.... hard....it's just hard work!"
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DON'T BE SCARED
-Stretch