Similar to jet lag, but with space ships. Traveling between mars and beyond (hopefully someone in the year 3000 reads this) will seriously screw up your circadian clock. Symptoms include needing a nap (or, if you're reading this in the future, a quick sleep in the cryo pods) and coffee.
Hey mom, it's Alec, I just landed on Mars and about to get to work mining with Dan! Need to grab some shut eye first, I'll call you back later, I've got rocket lag!