The practices are considered life threatening by Swedish police, according to Sveriges Radio (SR).
The hold involves pressing a person lying on their stomach to the floor and applying pressure on their back.
One witness told SR that she watched as a man in Södertälje was pushed down and soon had trouble breathing.
“He obviously put up a fight, he wanted to breathe,” said the witness.
According to the radio station, the man died after psychiatric staff held him down on his stomach for about 10 minutes.
An autopsy revealed that the victim had a serious heart condition and that his heart couldn't withstand the stress of the hold.
Those responsible at the Södertälje hospital deny that the man was subject to the restraint.
In another case, in Karlstad, a police investigation is ongoing in which the prosecutor will determine whether anyone should be charged in connection with the death of a mentally handicapped man in a psychiatric emergency room.
According to SR, the man had been pushed down on his stomach with his hands restrained behind his back.
A caregiver had tried in vain three times to alert others that the man couldn't breathe.