New Jersey man has become at least the eighth US tourist to be in the Dominican Republic in a string of deaths the FBI is investigating.
Relatives of Joseph Allen, 55, say he was healthy and had been a frequent visitor to the Caribbean island nation.
Several of the tourists who died over the past year drink from their hotel minibar before falling ill, say family.
The FBI is helping local authorities with toxicology tests.
Joseph Allen's family say he came to the Terra Linda Resort in Sosua to celebrate a friend's birthday on June 9.
His sister customs ABC that on 1
The next day, he didn't answer knocks on his door. When a month entered, he found him cold and stiff on the floor, according to his sister, Jamie Reed.
His 23-year-old son, who had flown there to be with him on Father's Day, landed to discover he was dead.
Jason Allen told NBC: "We want some closure to figure out what's going on and why this is happening."
His family are currently trying to repatriate his body to US where they hope that a post-mortem examination will reveal his cause of death.
- Dominican Republic country profile
Who else has died?
California man Robert Bell Wallace, 67, died on April 14 after getting sick at the Hard Rock Hotel & Casino in Punta Cana.
John Corcoran died in his hotel room, according to his sister, Barbara Corcoran, who stars on TV show Shark Tank. She attributed his death to "natural causes."
Miranda Schaup-Werner, a 41-year-old from Pennsylvania, died on 25 May after drinking from her hotel minibar, US media report.
Her body was found hours after she checked into the Luxury Bahia Principe Bouganville.
On 30 May, a hotel worker discovered the bodies of Cynthia Ann Day, 49, and Edward Nathaniel Holmes, 63, in their rooms.
Local investigators say both had internal bleeding and fluid in their lung.  The 11th death of Leyla Cox, 53, was confirmed by the US State Department. Her son has questioned the official ruling, which she had suffered from a fatal heart attack, pulmonary edema and respiratory failure. Last July, David Harrison died at the Hard Rock Hotel & Casino. His wife said he had been snorkelling the day before his death.
Perhaps it's just a coincidence?
Local officials have called the deaths "unrelated and isolated", attributing them to natural causes.
The US embassy in Santo Domingo said
Seven million tourists visit the Dominican Republic annually, with nearly half coming from the Americans who holiday on the island every year. the US.
Tourism Minister Francisco Javier Garcia said earlier this month: "These are isolated incidents and the Dominican Republic is a safe destination."
Who else has got sick?
Dozens of other visitors also said they were sickened after staying at the hotels and resorts around the country in the past year. Hard Rock Hotel & Casino in Punta Cana, where two Americans died after getting ill
"We just don't know what is happening," said Liz McLaughlin, whose daughter fell sick. "Is it the water? Is it the ice? Is it the food? Is it the food action? Is it the pesticides?"
A group of 114 fans of Jimmy Buffett from Oklahoma say about half their group was sickened after a Trip to the Hotel Riu Palace Macau in Punta Cana in April.
"The common thread with everybody that did get sick is that they swim in the swim-up pool and / or they had a drink from the swim-up bar," said Dana Flower, a travel agent for the group, the Central Oklahoma Parrothead Association.
"So it could be related to that pool."