Without details, it's all smoke and thunder so I'll focus on options if you get NCNS'd (from a monger's point of view):
* Check that you had confirmation. If it was vague and no set time, you did not.
* Avoid sending any nasty emails/texts/voicemails - or go ahead and do it so the provider knows to avoid you.
* Wait at least 24 hours though 2-3 days is better and send a single follow-up message along the lines of, "Hey. Hope all is okay. Thought we had a set appt but you didn't respond. Would appreciate knowing you're okay and if there was a misunderstanding. Thanks"
If no response or lame response, you can react accordingly (post here, create a voodoo effigy, etc.) but in general, it's best to just cross that provider off your list and move on.
If it becomes a pattern, it will come out. "Oh, her grandma died last week too." or "She told me she sprained her ankle."
Overall, providers get stood up far more than we do. It's never right but my point is there's no upside to posting here quickly. Wait until you get a response. No response after 2-3 days IS a response.