'Damaging effect'
Other participants spoke of stress, anxiety and depression brought on by assessments, and a fear of further changes.
Mr Neil accused the UK government's "austerity agenda and benefit cuts" of having a "damaging effect" on people in Scotland.
He added: "Their approach is slashing the incomes of some of our poorest households and pushing 100,000 children into poverty.
"The study is further evidence that people are living in constant anxiety about changes to their entitlements and are already suffering from the effects of around £6bn of cuts taken from Scottish welfare expenditure over the last five years.
"Despite these frustrations we will do all we can to use our new powers to make our system fairer and simpler and work to improve the experience for people."
'Safety net'
However, a spokesman for the Department of Work and pensions said the reforms were about giving people peace of mind.
He added: "Reforms to welfare are designed to help people into work, giving more people the peace of mind and security that comes with a steady income - there are now near record numbers of people in Scotland in a job.
"The government provides a safety net to support millions of people who are unemployed or on low incomes, spending £94bn a year across the UK on working age benefits.