A keen sportsman walked in front of a lorry on the approach to the Dartford Tunnel half an hour after disappearing from a nearby hospital, an inquest heard.
Oliver Hedges, 22, from Swanley, had been arrested twice within the previous 30 hours by police concerned for his safety.
On one occasion he forced a fast train to stop near Swanley station, and boarded the train trackside.
He told police he had tried to inject himself with bleach but it hurt so much he gave up.
Earlier he had phoned his former partner, Kylie Inkpen, in a distraught state. She told the jury he admitted taking drugs and alcohol.
His mother, Beverley Brenchley, said he was a powerful rugby flanker and a keen bodybuilder.
He changed after his playing career was ended in 2007 by an injury that needed daily medication.
Later he admitted he had taken cocaine, but his personality rapidly altered after he injected steroids.
An 11-member inquest jury was appointed to investigate how he died after being taken into hospital care - and how he got away from the Littlebrook hospital where his mental state was being assessed.
This was later reduced to 10 members when one juror applied to leave the hearing.
A post mortem revealed Mr Hedges had consumed a large amount of alcohol and used cannabis shortly before his death in the early hours of October 31, 2010.
The inquest continues.