An NHS trust has started an inquiry into the death of a man 48 hours after he dialled 999 asking for an ambulance because he felt unwell.
Jonathan Dear, 46, from Southend-on-Sea, told emergency control room staff he was "weak and about to collapse", but no ambulance was sent.
He was found by a family member 48 hours later.
The East of England Ambulance Service NHS Trust (EEAS) said the 999 call had been categorised as non-emergency.
A spokesman for the EEAS said it was in the early stages of an investigation.
A spokesman for Essex Coroners' Office said the circumstances of the death were still being investigated and a decision on whether an inquest was needed had yet to be made.
Neighbour Patricia Sampson described Mr Dear, an alarms technician, as an "easy-going, fun-loving, bubbly man who cared for his community".
"I was absolutely shocked to discover that John had passed away, particularly under the circumstances that an ambulance didn't come at the time he called for one," she said.
The ambulance service spokesman said it received a 999 call at 10:08 GMT on 15 March from a man who reported feeling "run down and weak".
"Based on the information provided over the phone, [it] was coded as a category 4 (non-emergency call)," he said.
"The patient was advised that we would not be attending and was advised to contact GP, pharmacy or attend A&E.
"At 12:46 GMT on 17 March we received a report of a man who was not breathing. A paramedic in a rapid response vehicle attended in 11 minutes. Sadly, there was nothing that could be done for the patient."