People with obstructive sleep apnoea (OSA) are having to wait up to two years for appropriate treatment.
About two million people in the UK have moderate or severe symptoms related to OSA, which makes patients temporarily stop breathing while asleep.
This can happen hundreds of times a night, leaving them exhausted, with poor memory and concentration and a significantly higher risk of accidents.
A recent spike in diagnosis has been linked to rising levels of obesity.
Paul Wilson, 72, from Essex, went to see his GP in April 2018 when he first began to experience chronic drowsiness.
It took nine months before he was given an appointment at his local hospital and then a further three months before he was able to see a sleep specialist.
"I was told I would be referred and was given the choice of five clinics, even though none of them had appointments available," Mr Wilson told BBC News.
"I then chased, after a few months, to no success and it wasn't until the following year that I was finally contacted about an appointment to see a specialist."
Test results showed Mr Wilson was stopping breathing about 56 times every hour while asleep and he was given a continuous positive airway pressure (CPAP) mask to wear while sleeping, which significantly improved his quality of life immediately.
"I was not aware how much it was impacting me and I had no idea how dangerous it was," he said. "It came as quite a shock.
"I'm not falling asleep during the day any more, I'm sleeping through the night and so is my wife now my snoring has improved."
Respiratory consultant Dr Annabel Nickol, who leads the sleep and ventilation service in Oxford, said patients with "disabling symptoms" were being left to struggle alone because services were at capacity across the country.
"There is a crisis facing sleep services in the UK," she said.
"During prolonged waiting periods, patients are exposed to ongoing burdensome symptoms and the sixfold increased risk of having a road traffic accident due to loss of concentration or 'micro-sleeps' behind the wheel.
"If patients are advised to discontinue driving until they receive effective treatment, they may have significant loss of independence or even loss of employment."
People should consult their GP if they have loud snoring, pauses in breathing at night, excessive daytime sleepiness or fatigue and sudden awakening at night.