Being a patient is a "full-time job", say researchers, because more people are likely to have multiple conditions.
The Academy of Medical Sciences said doctors were seeing a clustering of different physical and mental health conditions in a single patient never previously seen together before.
It means people can end up battling heart disease, breathing problems, osteoarthritis and depression together.
Researchers warned that the NHS and other health systems were not prepared.
They added this was a global phenomenon and said that doctors and nurses were too often focused on a single condition.
This approach leads to patients having to attend endless appointments with different specialists and being placed on a cocktail of different drugs.
One of the researchers, Dr Lynne Corner, said: "It is a full-time job being a patient.
"You can have five different appointments, on five different days with five different teams. That's hard for patients and hard for their families."
She said the health service needed to get much better at treating the "whole person" rather than just individual illnesses.
Fellow researcher Prof Stephen MacMahon said he agreed.
He also said more research was needed to understand the causes and that while the ageing population and rise in obesity were undoubtedly factors, they did not fully explain the rise.
Over the last year, the number of over-50s in England with two or more conditions has increased from 32% to 43%.
"There is something else going on. We need to understand what to better invest in treatment and prevention."
The researchers also noted that even the young were being affected, with rising numbers of children and adolescents being diagnosed with type two diabetes – something which had been unheard of previously.
NHS England said it had already set out plans to end what it has called "fractured care".
This included the creation of accountable care organisations across the country, which involves hospitals, GPs and social care staff working together to create more integrated services.
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