Anyone familiar with respiratory sinus arrhythmia in the heart? Is this normal?

Last night I got really anxious for some reason and I felt my heart beating to how I breathed. For example I would breath out and it would slow down, then I would breath in and it would go fast for 3 or 4 beats then slow down as I exhaled. a month ago I wore a 24 hour holter monitor and I experienced this during the test and everything was normal. So what is this and is this normal in everyone?