The ambulance service is on the verge of "breaking down" because staff are suffering high levels of stress amid long working hours and tight targets, according to a new report.
A survey of 1,300 ambulance staff by Unison found that one in five described their work-life balance as "terrible".
A third said they had taken time off work in the past year because of stress, while some revealed they were "suffering in silence" because they were scared to report health problems.
Unison's head of health, Christina McAnea, said: "The Government needs to take work related stress in the ambulance service seriously or it will break down.
"Our members accept that their jobs can be physically demanding and challenging. However, some now tell us they are suffering from heart palpitations, flashbacks, nightmares, migraines, depression and an overall feeling of despair. As a result, many are actively looking to leave the profession.
"Last year, a third of ambulance workers experienced violence in the line of duty. Sadly, they are seen as easy targets especially late at night when the pubs and clubs turn-out.
"Stress is a silent time bomb ticking away and it is unacceptable that such high levels are part of normal life for ambulance crews. It is clear the pressure caused by funding cuts is having an impact on patient safety. Higher call out rates and lengthy waits outside A&E add to the problem."
Work related stress will be debated at Unison's annual healthcare conference in Brighton next week.
A Department of Health spokesperson said: "The ambulance service is performing well - arriving on scene in under eight minutes in more than 75% of the most life-threatening cases.
"But we know the service is getting busier so since 2010, the NHS has recruited 16% more paramedics to help.
"Longer term, NHS England is carrying out a review to look at demands on services and how the NHS should respond.
"Violence against NHS staff is unacceptable. Employers must make sure staff are properly supported - we know that staff who are happier in their roles can give better care."