What your master seems to be experiencing is a form of "Dom Drop." It's not serious, although it is worrisome.

Some dominants, upon seeing what they've actually done to their submissives, feel deeply remorseful and become very emotional and even depressed over it. It is a perfectly normal condition, but one which requires a little TLC to overcome.

What you did was probably the best thing for him at the time. Just let him know that you are fine and that the situation was not nearly as bad as it looked.