I think Christmas truly captures this echo of our longing for something more than the material. Even when we've reached the pinnacle of our euphoria, our highest joy, even when (theoretically) we should be at our happiest, - i.e., during everything that happened yesterday - when we wake up the next morning, we still feel a sense of emptiness. We're on an emotional and mental sugar crash from all the ping-ponging emotions we felt yesterday. We feel a little lost, a little blue.
The Christmas high does not satisfy.
And that's why we were made for eternity. The ever-insightful C.S. Lewis:
If I find in myself a desire which no experience in this world can satisfy, the most probable explanation is that I was made for another one.
We were created to find the fulfillment of all of our desires in God. He is the one who leaves us with no kind of post-disappointment. Our weary soul finds needed rest in Him. Furthermore, it finds fullness of joy in Him. It finds hope and anticipation of a beautiful eternity in Him. It finds peace in Him. It finds grace and mercy in Him. It finds forgiveness for our greed and anger and worry and frustration and bitterness and depression in Him. It finds truth in Him. It finds eternal love in Him. It finds life and light in Him, light and life that motivate us to enjoy the good gifts that He gives us but not to try to find fulfillment in them.
We were made for satisfaction in God. On this ominous "Day-After," preach the gospel to yourself and remind yourself that the Christmas high does not satisfy - and that's okay.