Dale Earnhardt Jr.is opening up about the scary health crisis that lead to his retirement in 2017.

Appearing onGood Morning America, Wednesday, to promote his new book,Racing to the Finish: My Story, the former NASCAR driver revealed the scary symptoms of a head injury he suffered in 2012.

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“I got injured in 2012,” he explained. “That wasn’t the first concussion but that was the most serious one and I went and I got help.”

After treatment, Earnhardt Jr., 44, returned to racing, but soon the symptoms returned. “I started crashing again and just sudden symptoms were coming back after these crashes and they were getting more and more pronounced with each crash and I was trying to handle it myself,” he explains.

“If I had a crash and had symptoms — I would write a diary and, you know, how I felt after the wreck, how I felt that night, all the next day for several days and so that helped me kind of understand the progress of the symptoms and if they were getting better or worse,” he said. “And I started making a habit of this and ended up accumulating about 12 concussions in a very short period of time. It got to a point to where I couldn’t stand up.”

“It got to a point to where I couldn’t stand up, I couldn’t turn my head without falling over and my eyes were not working right focusing and tracking an object of a bird flying across the sky,” he explained. “It got so bad, so I finally said,’ I can’t drive, I can’t operate a racecar much less drive to the grocery store.’ ”

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The former driver details his head injuries in-depth in his book, which also features parts of the journal he kept to document his symptoms.

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Also in the book, Earnhardt Jr. addresses rumors that his wife Amy influenced his decision to walk away from the sport.

source: people.com