More than two-thirds of teachers lose sleep because of work pressures, which also cause many to turn to drink, drugs and overeating to cope, new research has found.
An inquiry into teachers' mental health by the NUT also found that more than one-third do not look forward to going into work.
A large majority said their work-life balance was a problem. Performance targets, over-detailed requests for planning and a rise in the number of classroom observations - cited by more than two-thirds of teachers - were particular concerns, the researchers reported.
More than 40 per cent of teachers surveyed said they resorted to alcohol, smoking, unhealthy eating or "other substances" to cope.
One teacher said: "My alcohol consumption is gradually increasing. I have taken prescribed drugs in the past and can see I'm going the same way again."
One-fifth of teachers were afraid of violence from pupils or parents, the study suggested.
Their remarks came in a detailed survey by Barnsley NUT to which 44 per cent of the union branch members responded.
Pete Bevis, NUT executive member for South Yorkshire and a member of the union's national working party on mental health, said he believed the results of the branch's research were a reflection of the picture nationally.
"There is no reason why Barnsley should be any different from anywhere else," he said. "If this is not a one-off, then it really does call into question what is going on with so many of our members affected by health issues."
There was also evidence that schools were breaking the three-hour annual limit on the classroom observation of teachers.
One teacher said: "In many cases, six 30-minute sessions turn out to be six one-hour sessions. Many are announced, but some of them are `drop-ins' - `drop-ins' that last 55 minutes."
Half of the teachers said they had difficulty coping with the pace of change in education, and more than a quarter had taken time off because they were anxious, depressed or unable to cope.