He wasn't expected to live.
But McMullin has not only survived - he's flourished. He's enjoyed a full and normal life as a married father of three living in Voorhees, N.J. Inspired by the professionals who helped him rebuild his life, he now works as a physical therapist at Manor Care in West Deptford.
"With some people, I use my story to help ease their pain and anxiety," he said. "No one wants to be in rehab. Sometimes I can help them get through it."
Despite Giffords' seemingly speedy and seamless recovery, she faces tremendous challenges, he said.
"The hard part before was for her family," he said. "Now, for her, the hard work is ahead."
Recovery is complex
There are two parts to recovering from a head injury. The first is surviving the initial insult.
In some ways, that's the easier one.
"When patients get to rehab, their family and friends tend to breathe a sigh of relief - 'We're through the woods' - but from a practical point of view, all of the things we take for granted, from zipping a fly to balancing a checkbook, can be a tremendous challenge for someone who's had a head injury," said Timothy Young, medical director of the Brain Injury Unit at Magee Rehabilitation.
"The first six months are a very labor-intensive period of time, and it's where the patient and the support network have to adjust to this major life-changing event."
The brain is an incredibly tricky organ. Even though medical schools teach a "map" of the brain and its functions, very few things are controlled solely by one specific part of the brain, Young said. That makes it difficult to predict how an injury will affect an individual.
"That's the biggest challenge with the treatment of brain injury," Young said. "Each individual's injury is going to affect each individual very differently. It's different from treating a leg fracture or an arm fracture."
Recovery depends on a combination of factors, Young said, including availability of health care, a patient's education level and personality traits before the injury, and the support that a patient receives from family and friends.
Recovery can take from months to years.
"People continue to face challenges," Young said. "You'll hear people say they're still making improvements two years out, four years out."
Ironically, the patient may not even remember the incident that caused the initial injury.
Giffords was conducting casual meetings with constituents outside a Tucson grocery store when she was shot. Jared Lee Loughner, 22, is charged in the shooting that killed six people, including a federal judge and a 9-year-old girl, and wounded 13.
This week, Loughner pleaded not guilty to federal charges of trying to assassinate Gifford and the attempted murder of two of her aides. He will face state charges dealing with the other victims later.
Giffords is being treated for fluid on the brain in the Neuro-Intensive Care Unit at Memorial Hermann Hospital-Texas Medical Center. She could move to a rehabilitation center by week's end.
When McMullin awoke from weeks in a medically induced coma, his first words showed that he had no idea what had happened: Seeing his police captain in the room, "I asked him for a day off because I had a headache," McMullin said.
"When I finally realized what had happened to me, I was blown away."
Shot in the head
It should have been a routine stop.
Don McMullin and his twin brother, Brian, were on patrol together in West Philadelphia on June 27, 1991. They pulled over a car about 2 a.m. at 57th Street and Washington Avenue.
There were three men in the car. Three men involved in the drug trade. One of them put a gun against McMullin's temple and fired.
As the car sped away, McMullin's brother struggled to save him with CPR. As he pressed on his brother's chest, he repeatedly screamed, "Donald! Donald! Don't leave me!"
"I can remember saying, 'I'm not going to leave you,' but it was in my head," McMullin remembered. "The words weren't coming out."
The hospital was just minutes away. When they got there, McMullin managed to grab his brother's hands and pull them away. He managed to say the words that had been in his head, "I'm not going to leave you."
Doctors weren't as confident.
The bullet had gone through McMullin's brain, which was starting to swell. Over the next week, there were multiple operations, including one to remove the bullet. There were fevers. There was dangerous swelling.
While McMullin rested in a medically induced coma, his family never left his side. They brought in his favorite music, like Eric Clapton. Now, they're able to joke about it: Maybe playing "I Shot the Sheriff" and "Knocking on Heaven's Door" wasn't the best idea.
"I could hear everything," McMullin said. "Even when someone's in bad shape, talk to them. With my whole family there, I thought I was at a big party."
McMullin's family was sure that if he survived, he'd be forever unresponsive. They began to make a schedule to figure out who would stay with him each day.
But a month after his shooting, he was preparing for rehab.
The man who shot McMullin, James Leath, was caught. He received a sentence of 22 1/2 years for the crime. He was later given a life sentence for drug trafficking by a federal judge. His two accomplices were also found guilty on federal drug charges and are serving life sentences.
Relearning basic actions
McMullin's rehabilitation process, almost a year long, was grueling. He did stretches both as an inpatient and an outpatient. Sometimes, he would spend the day at Magee, then come home and another therapist would visit him there.
He had to relearn even the most basic actions: how to order at a restaurant, how to plan his day and cook a meal, how to count change at a grocery store.
"At times, it just seemed like, 'How many times can we do this over and over again?' " McMullin said. "It's like mastering a video game. You master a certain level and then move on to the next one."
Although he was on his feet fairly quickly, he wasn't aware that there was a decided sway to his gait. Therapists had to work to get him walking straight.
Since McMullin could no longer drive, he had to learn to plan trips via public transportation.
He had to do things repeatedly to get accustomed to doing them right.
"Any time I came to a roadblock, which made me realize I was injured, there'd be grief," he said.
But he never quit.
"I never even uttered that word, 'quit,' " he said. "I believe if you work hard at anything, good things will come. . . . As long as I had my life, that's what mattered."
Brian McMullin said that it was hard to watch his brother struggle.
"Here was this big, strong kid, starting over again," he said. "It's hard on the family to see anyone go through this."
Still, the family learned an important lesson: patience.
"Rehab can't be rushed," Brian McMullin said. "The brain has to readapt and rewire and relearn how to function. That takes time."
You've got to be tough
Looking at Don McMullin now, it's impossible to tell he was once so severely wounded that doctors told his family to say goodbye.
But he's blind in his right eye and he has periphery issues with his left. He can't drive. He's constantly "scanning" - turning his head from side to side to enhance his field of vision - but the movements are so slight and subtle they're unnoticeable.
"I use the strategies I learned and they've become almost automatic," he said. "Sometimes, when I'm tired I might forget to use the strategies and I might bump into someone and it's like, 'Where did they come from?' "
He also sometimes has problems with what he calls "reading between the lines," picking up on people's visual cues, or missing their jokes or sarcasm.
"It's something you never think you could lose, but it can really be affecting," he said. "If you take everything at face value, you're missing a lot."
When he told his therapists that he wanted to go back to school to study physical therapy, they warned him that it wouldn't be easy after an injury like his. In fact, they compared it to trying to run a marathon with two broken legs.
McMullin was determined. He used the strategies he'd learned at Magee to tackle his courses: Writing everything down, tape-recording lectures and replaying them later.
"I learned that when you really want to learn something, you devote your time to learning," he said.
As Giffords begins rehab, she'll learn her own techniques for returning to her real world.
"Her husband said she was tough," McMullin said.
"That's a good quality. You've got to be tough. You've got to be disciplined. You've got to be open to these new ideas you're going to be given and you just keep working at it."