A man shouted "help me" and "get off me" as he was restrained face-down by police officers hours before he died, an inquest heard.
Leon Briggs, 39, died in 2013 after being detained under the Mental Health Act at Luton police station.
A jury was told one witness described the father-of-two as "like a child crying out for a toy" as he was held down by officers.
Another said he looked her in the eyes and said "please help me".
The jury has been shown CCTV of Mr Briggs skipping between shops and across roads, before two Bedfordshire Police officers handcuffed him and placed him in leg restraints on Marsh Road in Luton on 4 November 2013.
Mr Briggs was detained in a cell at about 14:25 GMT, but he became unconscious and was pronounced dead in hospital at about 16:15.
The inquest heard his primary cause of death was "amphetamine intoxication with prone restraint and prolonged struggling" with a secondary cause of coronary heart disease.
The inquest heard Wendy Hamilton was shopping when she saw one officer restraining Mr Briggs on his lower legs, with another on his shoulders, and a third appeared to be looking through his wallet.
Ms Hamilton said she "thought the amount of pressure being used was not needed", adding she heard Mr Briggs shout "get off me" and "why are you doing this to me?".
"He lifted his head from the pavement, he looked me in the eyes and said 'please help me'," she said.
She added when two paramedics arrived "around 45 minutes" after she first saw Mr Briggs, she was "surprised" they "did not check Leon at all".
She said he was later lifted into a police van "front first" and "face down", "like he was a bag of potatoes" or "like they were picking up a dog".
"They lifted him not in a rough way... but it was not very dignified," she said.
Another witness, Raja Khan, said: "Mr Briggs was crying out... but not in an aggressive manner... in a similar way to a child crying out for a toy.
"I'm not going to forget what I saw in regard to the restraint... I do not agree with how Mr Briggs was treated... it would have been fair enough if he was being violent but from what I saw, he was not."
Former chairman of the College of Paramedics, Andrew Newton, said paramedics on Marsh Road were likely to have had "inadequate knowledge" of dealing with acute behavioural disorder patients like Mr Briggs in 2013, due to a lack of national guidance.
But Mr Newton added Mr Briggs "received no meaningful medical care" because they failed to properly check his vital signs, and this "fell below the standards of care".
He said Mr Briggs should have been taken to hospital in an ambulance.
The inquest heard part of a statement from Sgt Loren Short, who said he told paramedics Mr Briggs had been detained under the Mental Health Act when they arrived.
Police Community Support Officer (PCSO) James Collings described Mr Briggs as "aggressive" and "nonsensical", and "shouting 'no, no' and snarling" while in the police van.
PCSO Collings said when he questioned whether Mr Briggs was on drugs, one officer said: "[He is] mental", and Mr Briggs replied: "Don't take the [expletive]", to which the officer said: "I'm not taking the [expletive], I just want to get you back and get you some help."
The inquest continues.