Yes, it has happened more than once to me that my therapist either thought he had replied or meant to reply, and something thwarted him in some way. I have found that I don't need to suffer wondering what is up if I just follow up and ask him again, and let him know that his non-response is really hurting me. I would be surprised if he were mad at you - sometimes people can have a moment of scatteredness or distraction, for example, and just drop the ball. I hope you can reach out to him and let him know how you are feeling.