When I was 7 or so, my mother and I took a trip to the UK. We bought a bottle of some orange flavored drink to take back to our hotel because I enjoyed the stuff.
For some reason, the store-bought stuff was pretty hard to get down and seemed a bit sweeter and more viscous than would be desirable. It took me about a week to realize that I was drinking undiluted orange-drink concentrate.
Upon reflection, it was within a year or so of that trip that I was diagnosed with ADD and began being medicated for concentration problems.
Did you stare at the OJ bottle because it said “concentrate?”
As a UK resident I remember a particular furore surrounding the use of tartrazine, an artificial food colourant (British spelling ;) that was popularly used in children drinks of this kind until around 20 years ago. It has links to ADD and hyperactivity and has since declined in use.
It is possible that this was the catalyst or even the cause in your case. It may also explain a lot of my own concentration problems ;)
Growing up diluting these concentrated drinks, known in the UK as ‘squash’ or ‘cordial’, I had the opposite problem when travelling abroad, in that bottles of squash or cordial tasted disgustingly weak until we discovered that they were already diluted.