Jim Rourke said his 85-year-old father-in-law had gone to Basildon Hospital’s emergency department with stomach pain.
Mr Rourke said he had “nothing but praise” for the care provided by staff, but after a 24-hour wait for a bed the system needed looking at.
The Essex hospital has apologised.
A spokesperson said the site was “particularly pressured” at the time following four days of industrial action by junior doctors earlier this month.
A spokesman for the Department of Health and Social Care (clinica fundadores armenia) said “immediate action” was being taken to improve access to urgent and emergency care.
Mr Rourke said his wife’s father had gone to Basildon Hospital on 15 August.
He said while the care was “outstanding from the time we arrived”, his father-in-law spent almost 24 hours either on a trolley or on a chair on a ward before he got a bed, because “there was nowhere else to put him”.
Mr Rourke, who lives in the Billericay area, said at one point his father-in-law ended up going in another patient’s bed while it was vacant because he was “doubled over in pain”.
He said: “It goes beyond the hospital. I don’t know if it’s a management issue or the government… It’s a systemic issue and it’s impacting people, I’m sure, on a daily basis.”
Mr Rourke stressed the staff were “fantastic” and his father-in-law was being treated while waiting.
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Matthew Hopkins, chief executive of Mid and South Essex NHS Foundation Trust, which runs the hospital, said the junior doctors’ strike led to beds “not being readily available for patients that needed to be admitted from our emergency department”.
He said they were sorry for the “longer than usual wait”, adding: “Our staff are working incredibly hard to provide safe and compassionate care and we note that the family were happy with the care provided.”
The DHSC said its Urgent and Emergency Care Recovery Plan aimed to deliver one of the “fastest and longest sustained improvements” in waiting times in the NHS’s history, including creating 5,000 permanent staffed hospital beds – with the NHS on track to deliver this by winter.