Or, if you're talking about a brand new post you made today - I've noticed you've made more than one post with variations on the same header - it could have been the same glitch that I encountered earlier.
I had a post replying in a thread and when I hit reply it simply vanished into thin air. Never appeared on the thread, no trace of it.
If that's what you're talking about, then I'm afraid the only thing for it is to make the post again. It didn't happen a second time to my post, so it should be okay, I think.
No idea what caused it and it hasn't happened to me since.
LabRat