During that time she had given up her job, lost her memory and suffered blurred vision as her addiction escalated.
By the time she returned to England, Susie (44) was taking 100mg of tranquilliser tablets a day – 25 times the recommended daily dose of just 4mg.
She lives in East Winch with her sister, Carol Watson, who went to meet her at Gatwick when she arrived home.
"We were really scared when we first saw Susie come off the plane. She was led off by a young couple after she had had a panic attack on the journey over," said Mrs Watson.
"She was unable to stand up straight and, when we brought her home, we could not leave her on her own. She got lost going for a walk outside our house and had to call police to find her way back – she had only gone a few hundred feet."
A Spanish doctor had prescribed her with Lorazepam, a legal drug, when she suffered depression after the birth of her daughter, Elizabeth, in 1982.
Over time Mrs Dent upped her intake of the drug as its effects wore off – her doctor would increase the dosage over the phone.
Lorazepam, which was the subject of a BBC TV investigation in the late '80s, is one of the most potent tranquillisers doctors can prescribe.
The drug is known to be addictive and withdrawal symptoms include anxiety, sweating and, in severe cases, seizures.
Mrs Dent said: "I was so naive at the time and trusted my doctor completely. I just had post-natal depression and nothing more than that. I should never have been given anything like it.
"When I came to England in September I knew I was dying and could feel it getting worse and worse."
After going to St Augustine's Surgery, East Winch, on September 8, Mrs Dent was taken straight to Lynn's Queen Elizabeth Hospital.
Doctors took Mrs Dent off Lorazepam and placed her on the less powerful sedative, diazepam. The effect was terrible. She said: "The night times were the worst. I had horrible cramps and my leg, arm and face muscles would all lock. I also had seizures, but they were almost the best times because I would lose my mind and at least there was no pain."
Mrs Dent was discharged from the QEH at the end of October and referred to the Community Alcohol and Drugs Service (CADS) in Lynn.
Her withdrawal from tranquillisers has been a tortuous process. Each week she reduces her daily intake of diazepam by around 2.5mg – if she stopped taking the drugs too quickly she could slip into a coma and die.
Susie's hands fidget nervously while she talks, but there is now no resemblance to the woman who was helped off the plane at Gatwick by strangers.
She said: "At the moment I'm just thinking about getting better.
"The people at CADS have all been so kind and supportive and the course they put me on is absolutely fantastic.
"I have a great amount of determination, but I could not have done it without these people. I want other people in similar situations to know help is out there."
Service manager at CADS, Mark Adeney, was shocked at the massive amount of drugs Mrs Dent had been allowed to take.
He said anyone not used to taking the drug would probably slip into unconsciousness and suffer chronic respiratory problems if taking Susie's dosage.
Mr Adeney said: "I think that unfortunately this sort of situation was all too common in the '70s and '80s, with dosage not being properly controlled, though less and less cases are now being seen.
"This drug does work in the right context, but only if given as recommended, in the right circumstances and for a limited time – however, that is a lot of buts."
Mrs Dent, who was born in St Germans, hopes to become a drug counsellor herself once she has got off the diazepam.
She said: "I feel angry towards the doctor who first prescribed this drug without keeping any control over the amount I took. Coming off Lorazepam has made such a difference. It has given me my life back."
Mrs Dent, who is divorced, lived in a village outside Gerona on the Costa Brava for 27 years before her return to England last September.
She speaks fluent Spanish, Catalan and German.