Does anyone know what can cause a severe blackout when I haven’t had that much to drink?

So I’ve been drinking for a few years and I’ve always been able to handle my alcohol pretty well, however last night I had some drinks with a couple friends at their apartment and I drank maybe half what I’d normally drink on average. That being said, I don’t recall a single thing that happened and according to my friends I could barely talk or walk and I collapsed and passed out cold. I’ve never had that happen to me even when I’ve drank a significant amount more than that. Does anyone know what could possibly be the reason behind it?