I did the same thing you did on and off for almost 4 years...sober for anywhere from a week to a month...Then I would go on a binge for a week or and then go cold turkey. Rinse Repeat...I started having frightening hallucinations at one point and could not sleep. I too worried about brain damage; wet brain specifically. Severe Anxiety is what it was...
I am happy to say I have healed very well over the past three years...but it has taken getting and staying sober.