David Lodge, 40, lived with multiple learning disabilities including autism, dyspraxia and dysarthria, which prevented him speaking.
In January 2022 he was taken to Hull Royal Infirmary after he was found severely dehydrated on the floor next to the body of his father Peter who had collapsed and died unexpectedly.
His sister Dr Keri Lodge, a consultant psychiatrist, said there was an "overwhelming lack of urgency" when her brother arrived at hospital.
"Any other 40-year-old man who had not drunk or eaten anything for days would be treated very quickly but with David there was none of that," she said.
"There was just this sense of: 'We will put you in this side room and keep you away.'"
A later inquest heard there were multiple failings in David's care.
He was not offered pain relief, basic examinations were not carried out, and he was transferred to an acute admissions unit instead of intensive care, where he died hours later.
"They were side-tracked by the fact he had a learning disability," said Dr Lodge.
"I think he would have been treated very differently if that wasn't the case and it's so hard to live with that knowledge."
A spokeswoman for Humber Health Partnership, the NHS trust which runs the hospital, apologised to the family and said its processes have been changed to ensure patients with learning disabilities receive compassionate treatment at all times.