Dominic Elliott, 23, was high on ecstasy and cocaine when he walked into a bathroom at the house in Bridlington, east Yorkshire, and apparently began drinking from a bottle of bleach filled with a 95% concentration of sulphuric acid.
Hockney's former long-term partner, John Fitzherbert, drove Elliot to hospital in Scarborough, but he is thought to have died during the 45-minute journey.
Fitzherbert, in his 60s, told the hearing in Hull how Elliott spent the day before his death watching films, taking drugs and drinking alcohol.
At one point the young man got out of bed, laughed hysterically and threw himself 10ft off a first-floor balcony.
"I've no idea why he did it," said Fitzherbert, who said he was in a nine-month relationship with Elliott before the latter joined Hockney's inner circle at his home-cum-studio.
"He'd been snorting cocaine and he seemed agitated. I just saw his feet go over. He went head-first. Afterwards he got up. He seemed OK.
"I calmed him down and he came back to bed and smoked more cannabis. I asked him what it was all about, but I never got to the bottom of why he'd done it.
"I fell asleep in his arms. He seemed calm and relaxed".
An assistant to artist David Hockney died after drinking acid at the painter's home.
Dominic Elliott, 23, had taken cocaine, ecstasy and temazepam before he drank the liquid and was rushed to hospital, where he died, an inquest has heard.
Mr Elliott was taken ill at Hockney's home in Bridlington, East Yorkshire, in March.
The artist was asleep at home at the time.
Hockney's former long-term partner, John Fitzherbert, told the hearing he drove Mr Elliott to Scarborough Hospital in the early hours of the morning.
He said that, during the day leading up to the incident, he and Mr Elliott smoked cannabis and drunk alcohol and Mr Elliott had also snorted cocaine.
The inquest continues tomorrow.
Tributes have been paid to David Hockney's assistant Dominic Elliott by members of the rugby club where he played, as a second row, in the seaside town of Bridlington following his reported death.
The man who died after apparently being taken to hospital from the home of artist David Hockney is understood to be Dominic Elliott, one of the painter's studio assistants.
Mr Elliott, the subject of a Hockney painting in 2008, had sat for the 75-year-old artist on more than one occasion at his work space in Bridlington, East Yorkshire.
The 23-year-old had been hired from the local area and had assisted the artist with equipment on his latest projects, including last year's headlining Royal Academy show.
It's being reported that a 23-year-old man has died after being taken to hospital from the home of the artist David Hockney in Bridlington.