Nope, you're not alone. It's the let-down after all the madness and rushing about to get everything perfect.
Our bodies kinda go into hibernation for a while. Probably a very natural thing. Sleep late a couple of times, stare out the window while drinking coffee while visions of...new quilt patterns dance in your head. Then get up and go outside, if possible, and get some exercise. If not do some inside to get your blood moving.
Or, when all else fails, go into your quilting room and sob into a fat quarter of your favorite colors.