Dale Earnhardt Jr. said his doctors believe his concussion-like symptoms started with his June 12 crash at Michigan International Speedway, though the effects unnervingly weren’t obvious for weeks.

“Obviously with my history of concussions, knowing the event I had in Michigan, that wreck right there is where they believe I picked up this issue,” Earnhardt said Monday night during an episode entitled “Concussion Discussion” on his weekly Dale Jr. Download podcast. “I didn’t feel anything that next week. The off week, I went to Germany (on vacation), went to Sonoma, ran good, felt awesome.

“It was strange these symptoms came out of nowhere. But we started doing a lot of digging, and they seem to feel confident this occurred in Michigan.”

Earnhardt underwent myriad tests to rule out other possible afflictions such as Lyme disease and an inner-ear problem.

He said his symptoms – vision and balance problems – and their gradual development make it impossible to put a timeline on his recovery.

“I’ve never had a concussion that came on weeks after the event,” said Earnhardt, who has missed the past three Sprint Cup races. “Most of them you feel it immediately, and then they get better over time, whether it’s 72 hours or a month. This has been the opposite.

“This is scary for me because of the way it’s been different. I’m having balance issues. I’ve never had balance issues before. The eye issues with the stability, I’ve never had that before.

“It started very slowly, gradually and continued to progress until it stopped and stayed where it is. I don’t know what that tells me about how long this process is going to be. I felt I had a good understanding of concussions in the past, but this is certainly a new one. They all have different symptoms and they all do react differently to treatment and they all have their own time and the length of the recovery is different for everyone.”

Hendrick Motorsports and Earnhardt haven’t announced if he will return this weekend at Watkins Glen International. An update from Hendrick is expected Tuesday or Wednesday.

Earnhardt said his vision problem, known as “gaze stability,” typically responds well to treatment, and he has been doing daily physical exercises at home.

“Those are the ones I like to do the most because I want my eyes to get better as soon as I can,” Earnhardt said. “That’s the part annoying me the most, so I work hard on the visual exercises.”

Earnhardt believes the gaze stability, which prevents him from fixing on a moving object at a distance while moving his head, is the main problem and is causing his issues with balance.

“I think as one cleans up and improves, so will the other,” he said.

Much of the prescription for healing has been more about environment than exercises.

Earnhardt said doctors have encouraged him to spend time in busy locations with noise and movement, forcing exposure to situations that cause the symptoms. It’s the antithesis of his treatment for the 2012 concussion that sidelined him for two races. Doctors then advised Earnhardt to rest at home and avoid stimulus, such as time on his computer and iPad.

During his recovery this time, Earnhardt has spent time at JR Motorsports, gone to the grocery store with his fiancée, Amy, and had lunch with his family in a crowded restaurant.

The goal is to increase anxiety, which has triggered Earnhardt’s symptoms.

“When I first got checked out and was walking into hospital lobbies and halls, that drives the symptoms pretty heavily,” he said. “After an hour or two, your brain calms down and regroups and gets a hold of the situation. Anywhere you go with a lobby and a lot of movement and chatter and things happening. You’re in motion, you’re observing a lot of different things. That really drives the symptoms up. So my doctor wants me to expose myself to that. … Don’t shy away from doing these things because you think it’s going to make you feel bad.

“Go there and if it makes you feel bad, that’s fine. Just don’t make yourself sick. Once you’ve had your fill of exposing yourself to heavy symptoms, get in a calm place you’re comfortable and get back to feeling great. Keep doing that. Expose yourself and recover, throughout the day. You’re basically re-acclimating yourself to things that are driving your brain crazy.”

Earnhardt said he has gotten impatient since the onset of the symptoms from the Michigan crash (video above), which also involved AJ Allmendinger and Chris Buescher (who won Monday at Pocono Raceway). The lack of improvement has been frustrating.

“You go to bed each night hoping each morning, you’re going to be able to tell a difference,” he said. “That drives you absolutely crazy.

“In the past you can feel this improvement and know you’re heading in the right direction.”

On difficult days, Earnhardt said he reaches out to his doctor to say, “tell me you can fix this. I need to hear that again today. He knows me well enough to know all I need is a little positive reinforcement.”

He said it was impatience that caused him to send a tweet Saturday that his symptoms had plateaued (instead of waiting to update fans on the Monday podcast).

“There’s days you feel positive,” he said. “There’s days you’re frustrated. That certainly comes and goes with the process.

“But I’m very impatient, and I want change now. I want improvement now. So I’m constantly texting my doctor, telling him everything I experience every day, going, ‘What can I do to get better tomorrow?’ He’s like, ‘Look, you’ve got to realize this might be a process.’ ”

The 13-time most popular driver said he has been transparent about his recovery because “it drives me crazy wondering what people are wondering,” and he has spent time at his No. 88 Chevrolet’s shop in part to reassure team members that he is “functional” and explain why he isn’t racing.

“It worries me that people don’t know what I’m dealing with and I want them to know why I can’t drive,” he said.

Earnhardt, 41, has a contract with Hendrick that runs through next season. He intends to race beyond that, but “I’ll worry about that when I’m well.

“I’ll talk to my doctors and say, ‘What do I have left as far as the racing?’ My doctors are confident they can make me stronger than I was before this event,” he said. “I want to race more.”