Hi bofhgirl,
I react similarly to what you have described. I get very excited about things I am passionate about, and I like to share my joy with others. I would have done the same thing you did, in response to the information you received about the "potential activities happening at your gym".
Like you, I get anxious when I am made aware that I have done or said something unacceptable. I will ruminate and/or shutdown for sometime, afterward. I have learned from experience, that there are certain people in my life, who I can allow myself to be 100% myself with, and, who will not squash me, or bring me down a notch (so-to-speak), or make me feel that my excitability is not acceptable in any way, but, I know this isn't the point of what you have expressed, necessarily.
In terms of the incident you experienced, I believe that, if there are reasons why people should not be allowed to pass information on, to others, then the information should not be provided to anyone, at all, to begin with, as there is no way to known that one must refrain from sharing the exciting news (logically speaking).
I personally, don't utilize social media, as it provoked intense anxiety in me, when I gave it a go. People are unpredictable, and I prefer to feel safe in my environment/with my emotions and reactions to things. I wasn't able to feel safe, good, happy or at peace, on the social website I experienced. I share my excitement, exclusively with those I know are safe to do so, with, and, who even, celebrate in my excitement with me. It is somewhat sad that we have to give our excitement/level of enthusiasm any thought, much less, go about it in that way, and, in real life, it can be virtually impossible for me to be conscious of, or control my excitement, as I react by jumping up and down repeatedly and verbalizing all of my happiness, but, I think the self-preservation aspect of doing so, on-line, or within other, unpredictable environments, is vital, at least it is for me, personally.
I have noticed that I have been able to be completely myself, here, on WP, so perhaps, you would find this a good social outlet to express yourself, fully, although, I do understand how impulsively it can happen, despite the fact that you might be in an unpredictable environment in that moment.
I hope you are feeling a bit better at this time - : )