Most people cannot be left alone with their thoughts for more than a few minutes without getting twitchy, research has shown.
Some would even rather be subjected to electric shocks than be deprived of any form of stimulation, scientists found.
In a series of studies, researchers asked volunteers aged from 18 to 77 to sit alone in a room with no mobile phone, reading material or writing implements.
They were expected to spend six to 15 minutes doing nothing but thinking, and then relate how they found the experience.
On average, participants did not enjoy it at all, no matter what their age and background.
In one experiment, 12 men and six women even took up the option of giving themselves an unpleasant electric shock to break the spell of inactivity.
Previously, they had experienced the same shock and agreed it would be worth paying not to have it again.
The US psychologists wrote in the journal Science: "What is striking is that simply being alone with their own thoughts for 15 minutes 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."
Another study in which people spent time alone with their thoughts at home found that many "cheated", for instance by listening to music or using a smartphone.
"They didn't enjoy this experience any more at home than in the lab," said Professor Timothy Wilson, from the University of Virginia, who led the research.
The fear of having nothing to do is not thought to be linked to the fast pace of modern living or electronic devices, said the scientists.
Surveys had shown that people generally prefer not to disengage with the world rather than suffer no activity.
"Those of us who enjoy some down time to just think likely find the results of this study surprising - I certainly do - but our study participants consistently demonstrated that they would rather have something to do than to have nothing other than their thoughts for even a fairly brief period of time," Prof Wilson added.