Sherine Iraqi, a lawyer for the Palestinian prisoners society, said that Shalabi can no longer stand, has very low blood pressure and has lost a lot of weight.
The lawyer had earlier met with the representative for female Palestinian prisoners Lina Jarbouni.
Physicians for Human Rights will visit Shalabi on Monday to examine her and try to get her admitted to hospital, Iraqi added.
Detainee Lina Jarbouni called on all human rights institutions and the Palestinian leadership to intervene to help Shalabi.
Shalabi, from the village of Burqin, is being held in “administrative detention,” a category in the Israeli legal system which permits imprisoning suspects for six months at a time without charge.
She entered the 33rd day of her hunger strike on Sunday.