Navalny, who is considered a flight risk by authorities, said he is woken eight times per night by guards announcing to a recording camera that he is still in his cell.
Jailed Kremlin critic Alexey Navalny has said his health was declining and accused prison authorities of "torture" through sleep deprivation, with allies saying they feared for his life.
Navalny is serving a two-and-a-half-year sentence on old embezzlement charges in a penal colony outside Moscow. Rights campaigners have described his prison as especially harsh, and Navalny himself compared it to a "concentration camp."
The 44-year-old was arrested on his return to Russia in January from Germany, where he spent months recovering from a near-fatal nerve agent poisoning in August that he blames on the Kremlin.
Navalny's allies raised concerns over his health after he complained of severe back and leg pain in recent days, and on Thursday he made a formal complaint through his lawyers of mistreatment.
"I believe that my deteriorating health is the direct consequence of actions and inaction of FSIN employees," Navalny said, referring to the prison service by its Russian acronym.
He said prison officials failed to provide the right medicines and refused to allow his doctor to visit him behind bars.
In another complaint Navalny, who is considered a flight risk by authorities, said he is woken eight times per night by guards announcing to a recording camera that he is still in his cell.
"Essentially I am being tortured through sleep deprivation," Navalny wrote.
Navalny's lawyers managed to visit him at his prison in the town of Pokrov around 100 kilometres (60 miles) east of Moscow on Thursday, after they were denied access to the penal colony the day before.
In a statement on Instagram, Navalny's wife Yulia said later on Thursday that her husband had been in pain for the past four weeks and appealed directly to Putin to set his critic free.
"What's happening right now is personal revenge and punishment," Navalnaya said.
"This should stop immediately."
She said Navalny began suffering from back pain in the Moscow detention centre and his condition only worsened in the Pokrov prison. Officials have however refused to allow him to be treated properly, his wife said.
'Afraid for his life'
Lawyer Olga Mikhailova said Navalny's condition was "extremely unfavourable."
"He is suffering from strong back pain and pain in his right leg," Mikhailova said in remarks on Dozhd television after visiting him.
"Everyone is afraid for his life and health."
Mikhailova said Navalny's right leg was in "an awful condition" and that he was losing sensation in it.
She said that on Wednesday Navalny had undergone an MRI examination in a hospital outside the prison but doctors did not release any diagnosis.
She demanded that he be transferred to Moscow for treatment.
Another lawyer, Vadim Kobzev, accused prison officials of adopting a "deliberate strategy to undermine his health."
The prison service earlier on Thursday insisted that Navalny has been checked by medics and that "his state of health was assessed as stable and satisfactory".
Navalny's arrest and jailing sparked large-scale protests, an outcry from rights groups in Russia and abroad and condemnation from Western governments.
The United States and the European Union have slapped sanctions on Russia for jailing Navalny and for allegedly orchestrating last year's poisoning, a charge Moscow has denied.
The Kremlin said it was not following reports of Navalny's health and had not requested information from prison authorities.
"The condition of convicts and people who are serving time in correctional institutions is being monitored by their administrations.
That's their job," spokesman Dmitry Peskov told reporters.
Navalny has been a thorn in the Kremlin's side for a decade by probing corruption among officials and leading large protests throughout Russia.
This week his team launched a campaign seeking his release and announced plans to stage what they said would be "modern Russia's biggest protest."
The team said they would set a date for the protest once 500,000 supporters have been registered with the website free.navalny.com
As of Thursday, 250,000 people had signed up.