I found out.
When I was finally diagnosed with chronic Epstein-Barr disease I was given an anti- viral medication that caused severe side effects. I won't mention the name of the medicine because the manufacturer would probably sue me. One of the side effects was a learning disability. At least I guess that's what you'd call it, since I'd already finished school.
At first I couldn't read even a paragraph and remember how it had started. My reading skills had always been at the 99th percentile, but all I could read and understand were simple picture books. Over a period of months that improved and I could read normal material again, but only if there was no background noise or anything else to distract me.
And I couldn't remember numbers or do even the simplest arithmetic for months.
That happened about twenty years ago and my reading seems to be almost back to normal. Background noise only distracts me if I'm reading something that requires intense concentration like a scientific or legal document, and I rarely read those. I'd guess my reading level is now at about the 80th percentile, which is certainly adequate.
However I still have a problem remembering numbers and there have been times when I was under stress and couldn't think of my own phone number. Math was always the hardest subject for me in school and my levels on aptitude tests were usually below the 70th percentile. Now they're probably far below that and I'm thankful for calculators and the automatic dial feature on phones.
So now I know how it feels to have a learning disability. It doesn't feel like anything. Being unable to remember a number or something I had read a few seconds earlier felt no different than forgetting other things, and everyone forgets things at times.