Resignations are usually given in writing, accepted by the board with a motion and vote, and the fact is put into the minutes . . . .
So the questions is : HOW did they decide it was a "resignation"?
If they said, "well, I guesss Mary resigned. Lets appoint or elect someone else" - that would be a kind of "acceptance" of the resignation, because they acted upon your verbal outburst. But if they have not "accepted" your outburst as a resignation, then it is not official.
If you really want your postion back, call someone (i.e. President ASAP) and say that you just had a melt-down, it was not meant to be a resignation, and will dispute any attempt to make it a resignation.
Next time, just say "I have to leave this meeting and get some fresh air.'