The incomes of people in Wales could be cut by £466m by 2029-30 as part of the UK government's disability welfare reforms, according to new analysis.
Data analytics company Policy in Practice told Walescast that almost 190,000 people are likely to be affected – 6% of the population.
Brian Evans from Swansea, who receives support for multiple health problems, said the uncertainty meant he was constantly anxious with "the worry of what's going to happen to me".
The Department for Work and Pensions said it would not compromise on protecting people "who need our support", and that reforms "will mean the social security system will always be there for those who will never be able to work".
Mr Evans, 62, receives the Personal Independence Payment (PIP) for which eligibility will be tightened under the reforms.
PIP was designed to cover the extra costs of being disabled, and Mr Evans uses it to run his mobility car, which he fears losing.
"I haven't got a television because I can't afford one, everything's being spent," he said.
"So if things are cut back any further I really don't know how I'll manage."
When the changes were proposed in March, First Minister Eluned Morgan asked the UK government for an assessment of their impact on Wales specifically.
The Department for Work and Pensions has published an impact assessment for England and Wales.
The analysis by Policy in Practice, which has been working with the Welsh government and local authorities in Wales to encourage people to claim the benefits they are eligible for, breaks down the impact of the reforms on each region.
Blaenau Gwent, Merthyr Tydfil and Neath Port Talbot were the worst affected areas per head of population.
Sam Fathers, of Policy in Practice, told Walescast that for some people the reforms could mean "knocking 60% of their income out in one hit" and cutting thousands of pounds per year among people on some of the lowest incomes in the UK.
But he urged people not to panic because the proposals were currently at the consultation stage.
The number of working-age people claiming health-related benefits in the UK has increased by 45% since 2019-20.
The UK government proposed the reforms to save £5bn a year by 2020-30, though the number of claims is still expected to grow.
Ministers have said the plans would offer a £1bn package of extra support for people to return to the workplace, with a "try before you buy" approach enabling people to try a job without automatically losing benefits.
