The hearing heard that two days before the fatal crash, Mr Dunner had celebrated Purim when he gave away £2 million to the poor.
His father, Councillor Aba Dunner, said that his son had been singing and dancing as he spent the night handing out cash to the needy.
The inquest was told that on March 22 he had been to synagogue twice before he left his family home in Golders Green, north London, for their holiday home in Bournemouth.
Mr Dunner, a father of nine, had been driving sons Chaim, 22, Boruch, 10, and family friend Ginette Silber.
His wife Esther was driving with other members of the family in a car ahead of them.
The crash happened when the rabbi overtook a Toyota Celica on the A338 into Bournemouth but clipped its front off-side, sending the Bentley out of control.
PC Charlotte Wales, of Dorset Police, said: "The Bentley made contact with the front off-side corner of the Toyota. It was a glancing collision but would have increased the rotation of the Bentley.
"The evidence suggests the driver of the Bentley over-steered but did not make an attempt to correct it or apply the brakes."
Chaim Dunner told the inquest it had been an uneventful journey to Bournemouth, during which the family had listened to Chasidic music on the CD player.
He recalled that at the time of the crash: "I was looking at my lap, most likely at my mobile, and I looked up and we swerved to the right, then left, then right and left again. I would say he was driving at about 75 to 80mph but he was fine. When we swerved, he was just driving away from the other car and he was trying to get back in control and then he went straight off."
Dr Peter Sharp, a toxicologist, found traces of cocaine in Rabbi Dunner's blood and urine. He said the rabbi had taken cocaine, but not an excessive amount, and believed he had taken it in the days leading up to his death.
Dr Sharp said studies in the US had shown that the effects of taking the drug before driving can lead to speeding, loss of control, causing collisions and high risk, inattentive driving.
When Bournemouth coroner, Mr Sheriff Payne, asked him if the cocaine would have affected Mr Dunner's driving he replied: "Sure, yes."
The policewoman present at the crash, PC Wales, said she could find no obvious reason why Rabbi Dunner lost control.
She said: "He had steered to the near-side but the reason for that I haven't been able to establish. I don't think it was a case of misjudging things.
"There must be another reason; he fell asleep or collapsed at the wheel or was distracted."
In recording a verdict of accidental death, Mr Payne said the cocaine had been a factor in the crash.
He told the Bournemouth inquest: "The post-mortem would seem to indicate no difference in his heart from that of any other person.
"We have to consider another factor. It came to light that he had cocaine in his system and one of the effects is that you become reckless and you do not perceive matters properly.
"I have to conclude that it must be a contributory factor in what happened."