It depends if both of you are tired..I mean what if it's late at night?
you could just fall asleep in each other's arms or something...it would show disrespect to just roll over and say good night then go to sleep..that's why you shouldn't do that...the only time you really have sex and then get up and leave is if you're at a high school or college party...most people usually do go to sleep after they have sex...