Callaghan was one of at least 39 people injured when a gunman opened fire at the beachfront Hotel Riu Imperial Marhaba, in the coastal city of Sousse. At least 38 more were killed in the attack, for which ISIS has claimed responsibility.
Speaking from her hospital bed, Callaghan told CNN she couldn't believe the terrible events unfolding around her on Friday.
"My right leg was laying across my stomach," she said, still visibly shaken.
But despite her own horrific injury, Callaghan said she knows she was lucky. A woman next to her in the panicked crowd was shot four times.
"This lady was bleeding so heavily. And I was laying in her blood trying to keep her awake," she said. "It was dreadful. I've never witnessed anything like it."
Hit by bullet, 'I felt a kick'
In another room, Ukrainian Nadezhda Vasilevna, 76, also lies injured. Like many of those in the hospital, she is still wearing the bracelet that identifies her as a guest of the Imperial Marhaba Hotel. Doctors said they removed grenade fragments from her thigh.
"My husband went to swim, and I was lying and reading the newspaper by the sea. Suddenly I heard an explosion," she said.
"I saw the man running and shooting. He shot at us. For those who moved, he fired again. I looked where he pointed the gun. When he aimed the weapon in my side, I felt a kick. The bullet went right through my soft tissues."
She tied a towel around her leg and tried to hide in the sand, watching stunned as the gunman continued to fire.
"I was lucky," Vasilevna said. "I had no fear. It was like a movie. I just watched him and tried to deceive him. I just lost a lot of blood."
Meantime, Vasilevna's husband, Igor Vladimirovich, 78, watched the attack in horror from the water where he had been swimming. "The terrorist fired almost without stopping. He moved quickly," he said.
It was the couple's second trip to Tunisia.
Belgian Claude Pesser said he was very close to the gunman but remembers little about him — he was just too scared.
An X-ray image clearly shows the bullet that struck Pesser's leg, cutting him down as he tried to run to safety.
Pesser said he usually travels to Tunisia twice a year — but no more.
He expressed sorrow for his Tunisian friends, who he said are good people. But he said the situation in the country is now too dangerous and he thinks it will stay that way for a long time.
Thousands of tourists have been fleeing Sousse since the attack. On Sunday, a spokeswoman for Riu hotels said around 40 tourists remained at the Imperial Marhaba and that the company intended to keep the hotel open.
Tunisia's tourism industry had been beginning to recover since the 2011 Arab Spring, but the attack in Sousse — coming just three months after an attack on the Bardo Museum in Tunis — is likely to deal it yet another blow.
On Saturday night, a large crowd of Tunisians turned out at the hotel in a display of unity after the attacks. They chanted and sang, waved the red and white Tunisian flag and lit candles at the spot where the dozens of victims had been shot the day before.
ISIS has claimed responsibility for the attack, but it is unclear if the Islamist group had any direct role in it.
ISIS has posted a photo of the alleged attacker, whom Tunisian authorities have identified as Saif Al-Deen Al Rezgui, 24, from the town of Gaafour, about 160 kilometers (100 miles) northeast of Sousse.
Initial reports Friday about the attack suggested there had been three gunmen, but a Tunisian Interior Ministry spokesman later said the ministry was aware of only one and that he had been killed.
The spokesman, Mohammed Ali Aroui, told CNN on Saturday that the gunman specialized in electronics in pursuing his masters degree and didn't have any known relationship with a terror group.
Tunisian authorities on Saturday began transferring the bodies from Sousse to the capital, Tunis, the Ministry of Health said. It updated the death toll to 38 and said 39 people were wounded.
"The nationalities of the killed, most of them are British, German, and French, this is the 95% of them," according to Prime Minister Habib Essid. "The majority of them are British, then the second in number were German, then third in numbers were French."
Fifteen of the dozens killed were British, and the number may rise, the UK Foreign Office said.
One Belgian, one German and three Irish citizens were also among the dead. Ireland's Foreign Ministry confirmed the death of Lorna Carty on Saturday, while the mayor of Athone on Sunday said a couple from the Irish town — Laurence and Martina Hayes — had also died. It is not yet clear whether they were killed immediately or died later from their wounds.
German Chancellor Angela Merkel spoke with Tunisian President Beji Caid Essebsi on Saturday, a German government spokesman said. Merkel expressed her condolences, the spokesman said, and both leaders agreed to cooperate more closely on the issue of terrorism.
In the wake of the resort attack, Essid announced a crackdown on what he called "illegal mosques."
The mosques were "spreading rumors and poisons to encourage terrorism," he said Saturday. "About 80 (mosques) will be closed … within one week."
Attacks also in France, Kuwait
Tunisia's nightmare came the same day as two fatal terrorist attacks in other countries.
A man caused an explosion at a chemical plant near Lyon in southeastern France after having beheaded his boss and leaving the head hanging on a fence, French officials said. Authorities detained the suspect.
And ISIS claimed responsibility for an apparent bomb blast at the Shiite-affiliated Al-Sadiq mosque in Kuwait's capital during Friday prayers, leaving at least 27 dead and more than 200 wounded.