Researchers in Virginia asked "college-students (to) spend time by themselves in an unadorned room (for 6 to 15 min) after storing all of their belongings, including cell phones & writing implements. They were typically asked to spend the time entertaining themselves with their thoughts, with the only rules being that they should remain in their seats and stay awake.
... simply being alone with their own thoughts for 15 min was apparently so aversive that it drove many participants to self-administer an electric shock that they had earlier said they would pay to avoid.
Research has shown that minds are difficult to control, however, and it may be particularly hard to steer our thoughts in pleasant directions and keep them there. This may be why many people seek to gain better control of their thoughts with meditation and other techniques, with clear benefits. Without such training, people prefer doing to thinking, even if what they are doing is so unpleasant that they would normally pay to avoid it. The untutored mind does not like to be alone with itself."
Wilson TD et al. "Just think: The challenges of the disengaged mind." Science 345 (6492): 75-7; 2014.