The 30-year-old took a knock on the head during New Zealand's 29-20 loss to Ireland in November and it kept him out of the way at the start of the Super Rugby Pacific season.
Barrett returned to the Blues squad for their round three win over the Chiefs and will open for the Auckland outfit on Friday against the Highlanders.
It has been a struggle for the two-time World Rugby Player of the Year, who he believes was potentially on his mind to hang up his boots.
Brother forced to retire due to shivering
"I know very well how retirement can be caused by an injury if it doesn't work out. My brother Ken had to give up his career because of this. I've seen a lot of good friends and teammates in the past. That's what I did," Barrett told the New Zealand Herald.
"I tried to stay positive — I'm usually a very optimistic person. I was trying to find alternative ways of getting on top of things, and I did.
"It's probably the closest I've come to retirement and I wasn't ready for it. I'm only 30, and I still have so much to give. Back to being fit and healthy, I'm here to come now." Grateful and hope to contribute well to the Blues this season."
After November's matches, All Blacks players get a chance to go home and enjoy a break before starting the next Super Rugby campaign in February, but Barrett's off-season was interrupted by persistent headaches.
"The hardest thing about it was not finding a cure," he said. "It's a million-dollar question with a lot of repercussions. It was disappointing.
“Usually the months of December-January are festive fun times where you decompress and spend time with friends and family. I did that, but it was annoying with headaches all the time."
Barrett said it was a "relief" to be back fit, but acknowledged there were concerns about suffering from long-lasting symptoms.
"There was a lot of doubt," he said. “Anyone returning from injury has that. It is something you have to work on and it gets better with time, training and play. That game on the weekend almost felt like the beginning. It felt so foreign because it was the first time I was back in a blues jersey.
"I had that cloud like 'Am I going to return from this setback - or is it?'. So it's a relief to be back. I'm looking forward to competing again and playing football in New Zealand domestically .
"There's a lot going on in the world so we're very fortunate to be playing in this environment.
“Whenever I train or play by myself I have high expectations because of where I have been in the past and where I want to reach. Usually, it takes me a while to get into my groove at the beginning of the year but It's a challenge I've been waiting for."