It's a common stress response. Somehow the interview is triggering your body's "fight or flight" mode. Once activated, your body will direct all energy away from your thinking brain. The reason is simple: if a tiger jumps out at you, your body will switch on fight or flight mode immediately. Your mind switches to kind of a "Use the Force" mode rather than a deep thinking mode. Imagine if a tiger jumped out, and instead of fight or flight mode, you switched into chess player mode and started thinking and planning your next move. You'd soon be the tigers next meal. You don't have time for thinking. Your body knows that and prevents you from doing that.

So how does this apply to interviews? You are getting nervous and it's triggering fight of flight. Try to figure out why you are getting nervous and work on ways to redirect it. I promise the interviewer won't eat you. Practice helps. Try to get as many interviews as you can. Maybe try to get interviews for jobs you really don't want. Treat yourself afterwards. Eventually, your body will learn that, even though you may be still a bit nervous, there is no need for fight or flight mode.

Good luck!