He walked over to his local public health clinic in the southern Spanish city of Malaga and was promptly diagnosed with deep vein thrombosis, in which a blood clot blocks off blood flow deep in the veins, a potentially fatal condition.
Frost, who has lived in Spain since 1991, received daily injections of expensive blood thinners for several months at virtually no cost to himself until his life was out of danger.
Now the 74-year-old is one of thousands of British retirees in Spain who fear they will be forced to move back to Britain if they lose their free access to Spanish public health care as a result of Britain's exit from the bloc.
"I couldn't afford to live here without free health care," he said as he sat on the sofa of his 13th floor apartment in central Malaga on Spain's Costa del Sol which offers sweeping views of nearby mountains.
"This is my home now. I want to stay here. I want to die sitting on a balcony looking at a view, watching a sunset, having a glass of red wine. Not in some miserable grey street in Manchester with grey skies and no view."
READ ALSO: Eight reasons why Spain is very worried about Brexit
'Worried and anxious'
Spain is the number one destination for British nationals living outside Britain, far ahead of France and Ireland.
The country is home to just over 300,000 Britons, around a third of them aged over 65. The figure rises to around one million if Britons who live only part of the year in Spain are included.
With British Prime Minister Theresa May expected to invoke Article 50 of the EU's Lisbon Treaty on Wednesday to launch the process of leaving the bloc, anxiety is running high among this huge expat community.
"Nobody really knows how it is going to go," said Julie Payne, 65, of Brexpats in Spain, one of several groups that lobbies to protect the rights of Britons living in Spain, as she sat by the pool of her seaside villa in Benalmadena up the coast from Malaga.
"People are worried and anxious," added Payne, who moved to Spain in 2000.
Aside from fearing the loss of free health care, many retirees fear their pensions will take a hit when Britain leaves the EU, she said.
READ ALSO: Why Brexit is a 'matter of life and death' for some Brits in Europe
'Cutting out luxuries'
Under existing rules any British state pensions collected in Spain or any other EU nation get the same annual increase to compensate for inflation as those collected in Britain.
But it is not clear if this arrangement will be kept after Britain leaves the bloc.
The annual increases are not paid to Britons living outside of the EU in countries like Australia and Canada, whose state pension is frozen at the amount it was when they left Britain.
British retirees in Spain are already feeling the pinch from the drop of the pound, which has shed about 15 percent of its value against the euro since Britain voted for Brexit in a June 2016 referendum.
"For some this has meant cutting out on luxuries such as having a meal out. For others this means not being able to turn on the heating or cutting back on paying for personal care," said Kelly Hall, a lecturer in social policy at the University of Birmingham who has studied British retirees in Spain.
The drop in the pound was especially hard for the "numerous" British nationals living in Spain who are entirely reliant on a British state pension -- which is capped at around 480 pounds (€555 euros) a month -- as their only form of income, she added.
Spanish Prime Minister Mariano Rajoy says he thinks a deal can quickly be worked out with Britain to defend the rights of British expats in Spain after Brexit -- a view shared by Mark Sampson, the owner of the Eurobar in Benalmadena which sells pints of beer for just one euro.
"They wouldn't want us all to leave and take all of our money and wealth out of Spain," said the burly 50-year-old, who moved to Spain from the northern English seaside resort of Blackpool five years ago and voted for Britain to leave the bloc.
By Daniel Silva