Majuro , Marshall Islands ( CNN ) -- After showing signs of improvement , Jose Salvador Alvarenga 's health has deteriorated . Alvarenga , who said he was lost at sea for 13 months , returned to a hospital Thursday to be intravenously fed , said Christian Clay-Mendoza , a top Mexican trade official . `` Doctors say he 's severely dehydrated and low on vitamins and minerals , '' he said . Alvarenga , an El Salvadoran who had been living in Mexico , washed ashore on the Marshall Islands eight days ago . Earlier this week , his condition improved enough that he was released from a hospital . Doctors said Alvarenga 's limbs have started to swell , and they ca n't seem to keep him hydrated . But he did manage to leave the hospital briefly Thursday to make a few comments to the media . Bewildered by all the cameras , he thanked the government and people of the Marshall Islands for their care and friendship . After his minute-long remark , officials whisked him back to the hospital . Plans for his repatriation to El Salvador on Friday have now been postponed due to his health . Official : His story 'is probable ' Alvarenga 's claims have garnered widespread skepticism about how he could survive for 13 months adrift on the Pacific . But from what officials can tell , they have no reason to doubt him . `` The investigations into Mr. Alvarenga 's story so far have been substantiated , '' said Phillip Muller , the Marshall Islands ' foreign affairs minister . Clay-Mendoza said Alvarenga was an undocumented worker in Mexico . But `` what he has said to us about his identity , so far , has been true . '' `` We 've had contact with his family in El Salvador , and they have corroborated his story , '' the Mexican official said . `` Now we are trying to contact his boss at the fishing co-op he belonged to in Mexico , but so far everything he 's told us has jibed . The main question now is how long was he at sea ? '' Clay-Mendoza said `` it 's probable '' Alvarenga really did get lost at sea starting in December 2012 . He said the boat was reported missing in 2012 . If Alvarenga 's story proves true , the trip across the Pacific would have taken him across roughly 6,600 miles ( 10,800 kilometers ) of open ocean before ending in the Marshall Islands , about halfway between Hawaii and Australia , in the northern Pacific . Officials : 'We gave up ' trying to figure out how long castaway was adrift in Pacific . The other man . Alvarenga says he set off on a fishing trip from the port of Paredon Viejo , Mexico , near the southern coastal city of Tonala . He said he and another man intended to spend a day trying to catch sharks , but they were blown off course by winds and then got caught in a storm , eventually losing use of their engines . Bellarmino Rodriguez Beyz , the owner of Alvarenga 's boat in Mexico , identified the fishing partner as 23-year-old Ezequiel Córdova . Alvarenga said that four weeks into their drift , his companion died of starvation because he refused to eat raw birds and turtles . Eventually , he threw the body overboard . `` What else could I do ? '' Alvarenga said . Living on faith and fish . A grieving family . Back in the Mexican village of El Fortin , Córdova 's family is inconsolable . More than a year after the young man went missing , his mother is grieving his death . `` The pain is so great , I ca n't explain it , '' Córdova 's mother said . `` Losing a child is the hardest thing to bear in life . '' Córdova 's brother said the 23-year-old took care of his family -- and that 's why he became a fisherman , in hopes of earning a better livelihood . `` My brother was kind , he was responsible for my mother , '' he said . `` In fact , he worked in the sea because of her . He wanted to improve himself . He did n't want to be poor , like us . '' The fishing cooperative that Córdova and Alvarenga belonged to has about 45 boats , Rodriguez said . The fishermen make about $ 150 a week . But the waters near Paredon Viejo are notorious for the dangerous winds that can blow fishermen away . Now that Córdova 's mother knows her son is dead , she wants answers . `` As a mother , I demand the authorities allow me to talk to the survivor , '' she said . `` Only in that way will I know what happened , and what he did with the body of my son . I deserve to know the truth. `` Meanwhile , Córdova 's bedroom , scant with just a blanket as a headboard , remains untouched . Just the way he left it more than a year ago . This teen was adrift at sea for 26 days . Suzanne Chutaro and Jack Niedenthal reported from Majuro , Marshall Islands ; Holly Yan reported from Atlanta . CNN 's Nick Parker and Jethro Mullen also contributed to this report .
NEW : The mother of the dead diving partner asked to speak with Alvarenga . Jose Luis Alvarenga said he was lost at sea for 13 days . He has returned to a hospital due to exhaustion and malnutrition . Alvarenga said he had to toss his companion 's body overboard after he died .