People spend nearly half of their waking hours not thinking about what they are actually doing, according to a US study conducted via the iPhone.
More than 2,200 volunteers downloaded an app which then surveyed them about their thoughts and mood at random times of day and night.
The Science study suggested minds wander, even from demanding tasks, at least 30% of the time.
A UK expert said other studies confirmed people are easily distracted.
The iPhone was a novel research tool for researchers at Harvard University.
Participants agreed to be contacted, at which point they selected what they were doing from a menu, whether they were actually thinking about it, and how happy or sad they felt.
Remarkably, some participants were prepared to answer the survey even when making love.
While their study sample was composed entirely of people who owned the device, and were prepared to download and be disturbed by an app of this kind, the researchers said it provides an insight into how our minds can wander during the day.
After gathering 250,000 survey results, the Harvard team concluded that this group of people spent 46.9% of their time awake with their minds wandering.
Dr Matthew Killingsworth, one of the researchers, said: "Mind-wandering appears ubiquitous across all activities.
"This study shows that our mental lives are pervaded, to a remarkable degree, by the non-present."
In addition, the survey data on happiness appeared to show a modest connection between the degree of mind-wandering and the level of happiness.
People who were most distracted away from the task in hand were more likely to report feelings of unhappiness.
Reports of happiness were most likely among those exercising, having a conversation or making love, whereas unhappiness was reported most while people were resting, working, or using computers.
Dr Killingsworth said: "Mind-wandering is an excellent predictor of people's happiness."
However, whether mind-wandering is the cause, or the result of unhappiness is still not proven by the research.
Professor Nilli Lavie, from the Institute of Cognitive Neuroscience at University College London, said that while any attempt to try to measure the wandering mind was "heroic", the results of the study might be rendered less reliable by the type of participant it attracted.
She said: "Mind-wandering may simply be ubiquitous in the type of person who is engaging in this type of iPhone application, and who is prepared to be distracted from whatever they are doing in this way."
However, she said that her own laboratory research had found similar or even higher levels of mind-wandering among subjects given less demanding tasks to complete.