No problem, just age, and I found that as I got older, I became mildly allergic to the yeasts and grain in beer, so while I still love the taste and feel of good beer, I get headaches from it, so I found if I just have one or two, I avoid the headache. Distilled spirits, especially when aged 10 or more years in oak seem to avoid this problem. Love my Bourbon. Lately have been enjoying Evan Williams Single Barrel, aged 10 years. My all time favorite was the 2011 release of George T. Stagg, 15 year old bourbon, cask strength. The smoothest bourbon I ever had. I'm sure there are others as good, I just haven't sampled them yet.
Most of my life I subscribed to the old phrase "Excess in all things, moderation is for Monks". My philosophy hasn't changed from that except to include "avoid headaches".