The survey of youngsters not in education, employment or training (NEETs) found a third had experienced depression and more than a third "rarely left the house". The poll examined views of some 1,000 youngsters aged 16-24 across the UK.
The UCU's Simon Renton said it showed the "personal impact" of unemployment.
There are about 900,000 young people classified as being NEET and the lecturers' union survey provides an insight into how they see their circumstances.
It reveals that many feel isolated and are lacking in confidence - 40% feel they are not part of society, 36% believe they will never have a chance of getting a job.
One third have suffered depression, 37% rarely go outside the house and 39% suffer from stress.
Toni Pearce, president of the National Union of Students (NUS), said: "Long periods out of work or education not only have a devastating impact on individuals both in terms of their immediate health and well-being but have knock-on effects for the rest of their lives."
Mr Renton, the UCU's president, said: "It is truly heartbreaking to see so many people who want to contribute more to society but are left feeling their outlook is desperate and hopeless.
"The individual human tragedy is only part of the story as young people outside education or work cost the country millions of pounds every year. We need to give our young people a commitment of proper guidance and stable, properly rewarded jobs, or educational opportunities."
A government spokeswoman said: "Being out of work or education can be an enormous waste of a young person's potential. To tackle the problem the government is funding a place in education or training for every 16 and 17 year old who wants one, raising the participation age to 18, and investing in quality traineeships and apprenticeships."