Help! Random intoxication

I have never had this happen nor known anyone this has happened to. I was at the bar and I had a beer and a half, and all of a sudden I felt like I had done 10 shots. I got extremely light headed, woozy, and stumbled off the bar seat to the bathroom. I couldn’t make it and had to flag the bartender. He got me a seat and some water, and gave me some space, and i felt normal again within a few minutes. I had a light headache but was coherent verbally and with my thoughts again.

Does anyone know if this is signs of anything or just a freak incident? For reference, I can drink 4 to 5 beers generally before being half as intoxicated as I felt in that moment. I was not power drinking either, and that beer and a half was in about an hour of relaxing.