The organization released the records on Thursday ahead of a court ruling in Sweden to decide whether to maintain an arrest warrant for him.
READ ALSO: Swedish court upholds Assange arrest warrant
More than four years since Assange moved into the Ecuadorian embassy to escape extradition to Sweden – where he faces a police investigation into rape claims – WikiLeaks argued his confinement there needed to be brought to an end as a matter of urgency.
“Mr Assange's mental health is highly likely to deteriorate over time if he remains in his current situation… It is urgent that his current circumstances are resolved as quickly as possible,” said a report published by the organization on Twitter.
The 27-page medical report is attributed to an unnamed “trauma and psychosocial expert” in London and dated December 11th, 2015.
It comes ahead of a decision expected on Friday morning by a Swedish appeals court on whether to maintain an arrest warrant for Assange over the rape accusation.
The judges will decide whether to grant Assange's request to hear legal arguments on the European arrest warrant issued by Swedish prosecutors in 2010.
Separately, Assange has agreed to answer questions from Swedish investigators from October 17th in Ecuador's embassy.
The newly-released medical report, accompanied by supporting documents, is said to be based on interviews with Assange and includes comments from others at the embassy.
According to the report, Assange often goes up to 22 hours without sleeping, although he has access to a treadmill for physical exercise.
“Until June 2015, Mr Assange felt himself to be resilient but significantly degraded…,” the report said.
“Since June 2015, however, his physical condition has deteriorated due to limited range of movement, inability to exercise normally and constant pain,” it added, quoting the unnamed expert.
Medical complains outlined in the report and also the records included pain in his right shoulder and dental pain from a fractured tooth.
One of Assange's colleagues was also quoted as saying that it had been difficult to find doctors willing to examine the WikiLeaks founder at the embassy.