Lawyer Hanin al-Khatib told Ma’an that Abed al-Majid Khdeirat is suffering from a kidney infection, breathing problems, and severe back pain.
Israeli prison guards punished Khdeirat by not allowing any visits for 6 months and banned him from buying anything at the prison canteen.
Guards are always using psychological intimidation to force him to end his hunger strike, his lawyer said. He has lost 27 kilograms since beginning his strike action on July 1.
Khdeirat, 45, is from Tubas and works in the PA national security forces. He spent 11 years in an Israeli jail before being released in the Shalit swap deal.
He was rearrested in May.
Another Palestinian hunger striker, Hussam Matar, is also in a serious condition and is currently being treated in hospital, PA lawyer Karim Ajwa said.
He suffers from kidney and liver problems and has lost 33 kilograms since launching strike action on June 1.
Matar, from Jerusalem, is sentenced to life imprisonment and is demanding better visitation rights, clothes and conditions for sick detainees.