Learning to walk...and giving me a heart attack

So my son is 11 months and is learning to walk and so far the last two days back to back he has fallen backwards and nailed his head hard on the floor. If we had carpet I wouldn’t be so concerned but we have cement flooring covered by vinyl tile flooring. And when he hits he hits hard and it’s been the back of his head both times. I’m just worried because it has been the same spot. I keep trying because to call the pediatrician to ask about it but they haven’t called me back so I’m thinking maybe its not a concern? Is anyone else’s babies who are learning to walk hit the back of their heads like this a lot?