Kevin Holt, 29, spent five years in the Army and served in Afghanistan and Iraq before being discharged in 2010 after being diagnosed with post-traumatic stress disorder.
He was discovered by his mother Shirley on July 13, 2018.
She has now called for "more support" for veterans in the wake of his death.
Mr Holt, from Thorne, South Yorks., told counsellors at Rotherham Doncaster and South Humber (RDASH) mental health service he felt extreme guilt over the incident nine years ago.
In a statement which was read to Doncaster Coroners Court, Linda Crossland, of RDASH, said: "He said he was not sure he could ever get over it.
"He said he felt extreme guilt that so many colleagues had lost their lives despite being commended for his behaviour and ensured that he did all that could be expected of him."
Mr Holt made four self-referrals back to RDASH, reporting anxiety, low mood, flashbacks and nightmares and was awaiting a further appointment at the time of his death.
Assistant Coroner Louise Slater heard he was packing his bags to spend the weekend at Help for Heroes’ Tedworth House recovery centre when he died.
He had also just been given the all-clear and was awaiting a final operation at the time of his death.
She said: "Kevin always wanted to join the Army and did in 2005 and he left in 2010.
"This followed an incident in 2009 when his friends from his regiment were killed or seriously injured.
"When he left the Army he didn't receive much support but this changed when he got counselling at Catterick."
Ms Holt said the cancer spread to his lungs and stomach but he was given the all-clear before his death and was awaiting a final operation at the time of his death.
Mrs Slater also heard he was prescribed zomorph as a pain killer for stomach pain associated with the cancer.
A post-mortem examination found he had more than ‘lethal’ levels of morphine in his blood, which Dr Paul Smith, a forensic toxicologist, said would have been from the zomorph.
PC Emma Cleghorn, who was called to Meadow View Caravan Park, Thorne, where Mr Holt lived on the day of this death said three empty blister packs of the drug were found in the caravan.
She said there were no evidence of suspicious circumstances surrounding his death.
She said: “Kevin was in his bedroom and sort of crouched at the side of his bed and was almost halfway through packing his clothes.”
Recording a conclusion of misadventure, Mrs Slater said: “I have found there was no evidence that Mr Holt intended to take his own life with a deliberate act.
“In fact, the opposite seems to be represented by the evidence. He had bought a train ticket, he was going to go away for the weekend and he was in the middle of packing.”
Mrs Slater said the facts of Mr Holt’s death may never be known and added: "In all of the circumstances what I do find is that Mr Holt carried out a deliberate act in taking the medication and we may never know the facts.
“It's possible that he did take a few extra tablets with the intention of dealing with the pain but not with the intention of taking his own life.”
Speaking after the hearing his mum Shirley called for the armed forces to offer more support to veterans once they leave.
She said: “I don’t think there isn’t enough support – I know there isn't.
“It shouldn't be up to the charities to provide all the help. The Army need to do more.”
Paying tribute to her son she said: “He always wanted to be in the Army. As a kid he was always in the garden playing with Action Men.”