Sam saves the night / by Shari Simpson.

Enhanced descriptions from Syndetics:

What would you do if you could stay out all night and not get in trouble ?
Thirteen-year-old Sam has no friends, but you can't really blame her. She lives her life in a state of chronic exhaustion thanks to her nightly sleepwalking jaunts, which include trips to the store, treehouse-building projects, and breaking-and-entering escapades--none of which she remembers in the morning. Her condition is taking its toll on her family (and her life), so when her mom takes her to see a wacky strip-mall sleep specialist, Sam is wary, but 100 percent in.
The night after the doc works his mojo, Sam wakes up outside her body, watching herself sleep. FREAKY! But once she gets over the panic attack, she realizes there's a whole world of detached-souls out there, called SleepWakers--cliques of kids like the Achieves, who use their sleep time to learn new things; the Numbs, who eat junk food and play video games all night long, and the OCDeeds who search for missing things and organize other people's stuff. And then there are the Mean Dreams, led by Madalynn Sucret, the nicest girl in Sam's school, who shows Sam that she can use her power to get back at a bully who's been tormenting her. Sam is intrigued--until it becomes clear that Madalynn is the real bully and the "tormentor" is just, well... sad. Now Sam is faced with uniting the various tribes of SleepWakers to fight back against Madalynn and the Mean Dreams in the most epic battle the night has ever seen.