Zack Dunlap opened his eyes within five days of receiving a severe head injury while riding an all-terrain vehicle without a helmet and walked out of a rehab center to return home 48 days after the November crash, NBC's "Today" reported Monday.

After the crash, Dunlap, of Oklahoma, was airlifted to United Regional Healthcare System in Wichita Falls, Texas, where doctors declared the 21-year-old brain dead.

"There was no activity at all. No blood flow at all," Dunlap's father, Doug, said of the PET scan he was shown by doctors.

However, Dunlap's cousin, Dan Coffin, who works as a nurse, decided to follow up on a hunch while a hospital nurse was removing tubes from the patient. He dug one of his fingernails in under one of his cousin's, causing Zack Dunlap to yank his arm away and place it on the other side of his body -- a sign of life.

"We went from the lowest possible moment to, 'Oh, my gosh, our son is still alive!'" his mother told "Today."

Dunlap said he still suffers from memory and emotional problems related to his injury but he looks forward to returning to his job as a warehouse worker and regaining his driver's license.