A hostage video released by Hamas terrorists of 21-year-old Israeli woman Mia Schem left her family relieved that after 10 days of knowing nothing of her fate, they could see she is still alive, but the footage also left them concerned that she is living in agony from apparent injuries and the fear they said was written all over her face.

"Until yesterday, I didn’t know if she's dead or alive," Schem's mother, Keren, told ABC News. "The only thing that I'm thinking about is my daughter. The only thing I think about is my baby."

The mother said that when she initially viewed the video Monday, she let out a scream of joy that her daughter was still alive and fell to the floor. Then she said she felt terrified, seeing her daughter's stitched-up right arm and realizing she had undergone an "operation alone without anyone to hold her hand, with terrorists around her."

Schem was one of the hostages taken by Hamas on Oct. 7 when thousands of armed terrorists crossed into Israel from Gaza and attacked a music festival she and a large number of Israeli young people were attending near the Gaza border. At least 260 victims were found slain at the music festival, according to the Israeli rescue service Zaka.

"I mean, this is the worst nightmare every mother can have," Keren Schem said.

In the video, Schem is seen prone on an upholstered chair with a flowery blanket covering her body as someone in a white coat and wearing latex gloves wrapped gauze around her injured arm that appeared to have stitches and a metal brace along her bicep. In another segment of the video, a similar blanket with the same flowery pattern was put behind her as a backdrop as she spoke into a camera in Hebrew, saying she was "fine" and asking her brothers to find a way to bring her home.

"It was hard for me to see my sister there. And I get the message clearly. I know what she wants me to do," Schem's 23-year-old brother, Eli, told ABC News.

He said he watched the video just once but knew from his sister's eyes that she was telling him, “'I need your help. And I need you to get me back home.'"

"That’s all I need from her," Eli Schem said.

The brother said that is why he is speaking out, to hopefully rally the world to demand the release of his sister and the roughly 200 other hostages Hamas is holding.

U.S. officials believe an undetermined number of the hostages are American citizens.

Eli Schem said the video sent him on an emotional rollercoaster. From the high of seeing his sibling alive one minute, and the next minute "you feel your heart like falling down."

Referring to the reported atrocities the terrorists committed in their killing rampage across southern and central Israel, he said that when he is alone, he can't shake knowing what "Hamas is capable of."

"That's the time you're like, starting to realize what happened. It's hard," he said.

While an expected Israeli ground offensive into Gaza has yet to commence, an Israeli military official told ABC News that specialized Israeli units are already in Gaza combing the territory for the hostages.

"We have special forces, regular infantry, artillery, tanks, armored divisions and battalions that are operating in that area, in the peripheral areas, conducting raids," Lt. Col. Peter Lerner, a spokesperson for the Israeli military told ABC News.

Lerner said the units are also collecting the bodies of Israeli civilians killed, to whittle down the number of people yet unaccounted for, explaining that was why the number of hostages believed held by Hamas climbed from 155 on Sunday to 199 on Monday.

One of the leaders of Israel’s hostage crisis told ABC News that 25 ambassador-and-up level, former diplomats, are working with every contact in Europe and North Africa, even Pope Francis, to pressure Hamas to release the hostages.

The group, according to the source, is being spearheaded by Yossi Cohen -- the former head of the Mossad, Israel's equivalent of the CIA -- and Yakov Peri, the former head of Shin Bet, Israel's version of the FBI.

John Cohen, the former acting Undersecretary for Intelligence and Analysis and Counterterrorism Coordinator for the U.S. Department of Homeland Security, said the Hamas video of Schem could yield the break intelligence officials have been seeking in their search for the hostages. The video is being closely analyzed by military and intelligence officials trying desperately to glean clues into the whereabouts of Schem and the other captives, from the furniture seen around her in the footage to the items on a nightstand next to her and the expressions on her face.

“Right now, military, law enforcement and intelligence officials are trying to build an intelligence picture that provides critical or vital clues on the location of the hostages, their well-being and any information regarding those guarding them that can aid tactical operations when they occur," said Cohen, an ABC News contributor.

Cohen said that when he viewed the Hamas hostage video of Schem, several things stuck out.

"One is any information that provides insight into the conditions of the hostages. Second, any information -- the background, the lighting, furniture -- that provides insights into the location of the hostages," he said.

The video also contains what sounds like explosions going off in the background and horns honking, which might tell investigators if the hostages are being held above ground or below ground in a maze of tunnels under Gaza that Hamas has constructed.

"The expression we use in these types of tactical operations is you want to ‘Find, fix and finish,' which means you want to locate where the hostages are. You want to develop a pattern of life around them. You want to look at how those guarding them behave, how they arrived where they are. Do they stay there? Anything you can that will give you an advantage in a tactical situation."

He said investigators are likely analyzing the method the video was released, and whether the terrorist network posted it online with accompanying identifying data or used some other way of making it public.

“Does that allow you to use geolocation types of technologies to pinpoint the location of the hostages?" Cohen said.

He said clues could also be gleaned from Schem's expressions, gestures, and words.

“They’ll look for hidden meaning in the expressions or in the words that are being used by the hostage, but generally the underlying belief is that whatever they’re saying they’re being forced to say," Cohen said. "But there is value, also with the physical condition. Does it look like they’re being abused? But again, mostly when they do proof-of-life videos they will clean people up and they’ll make them look in the most presentable condition possible."

Meanwhile, Schem's mother, Keren, said she has faith that the Israeli military will rescue her daughter.

“I know that the Israeli government and the Israeli Army are doing all they can to bring Mia and all the hostages back home," the mother said. "You know, we've been through so many crisis and wars. We are unfortunately used to it. So, we know what we're doing well. We have the best army in the world."

Asked what he would tell his sister if his words could reach her, Eli Schem said, "We love you so much. Don't worry we are coming to take you back home."