Ever just completely blanked during an interview?

Today had my final round for my top choice and I was simply going through the "why us" question and midway through my (rehearsed x1000) response I completely lost my train of thought and straight up said "sorry I just completely lost my train of thought" and then after a couple seconds of "umming" continued to the rest of the answer, fumbling a bit along the way. Didn't get a great night's sleep but has never happened to me before and I'm not a nervous person. After that question he was just like "ok that's the last question I have for you" (was about 15 minutes in for a 30 min interview) and I managed to ask him questions that lasted probably around another 10-15 minutes before leaving. It was probably my last opportunity for the interviews I've gone through so far and as a junior i'm pretty disappointed. It's a learning experience so I'll try to be less of a tard going forward but I was wondering if this has ever happened to you guys so I could shit on myself a little bit less today.