Returning from a big trip is always a letdown. Sure, you get to sleep in your own bed and you don't have to live in the same three outfits anymore. Sleep cycles are disrupted, of course, but it's bigger than that.
A long time ago, I wrote in a trip journal about how it feels. It's like the normal world is one of those wooden toy boards with different shaped holes in, and each person is a peg that has to fit in their own slot in the board. When you go on a big trip, you do all these new things, you see who you are without the creature comforts of everyday unchallenging life. You grow new bits and pieces, you expand and feel an awakening of the possibilities.
Upon your return, the hammer of life tries to force your now-explanded shape back into your slot. It's uncomfortable, because you've got new things about you that the normal world doesn't care about, wants to eliminate, wants to get you back, complacent with dullness. And eventually, you can't resist and succumb; sliding back into your place.
You never get back to complete normal, though; the scars of your experiences remain as a testament to the new growth that you sought. Sometimes those scars fade until you barely remember them; other times they scab and bleed and they're all you think about. Or they seem to have healed, but flare up and remind you--hey! over here! look what you've done! look what you're capable of! normal life doesn't have to be the end-all be-all!
It's disappointing because other people can never really understand the change that you go through. Too many people never travel; worse, too many people never *want* to go anywhere. And let alone going anywhere alone! If you are lucky enough to go somewhere with other people, you'll share that bond, that brotherhood, forever. You got to see and grow and wonder together, and you'll all understand the difficulty of returning home after an amazing new experience. Most of all, those fellow travelers understand the pull of wanderlust.
You have changed, but when you get home, nothing has changed. Your room is still messy and the city is still dingy. You still have to do the shopping and the dishes and go to bed at a reasonable time. You still have to make small talk and condense your adventure into twenty interesting, yet nonthreatening, words. The alarm in the morning doesn't signal the start of another adventure; it signals Just Another Regular Day. Not something to be looked forward to, not something to document with photos and an internal narrative, not something that holds the potential of New and Different and Exciting.