Wow!  Sorry to hear what happened - it's awful and unfair.  With everything you told us, I wouldn't be surprised if your boss wasn't telling you the whole truth about "why" this happened.  Don't let that bother you though, 'cuz that's their problem, not yours!  It's too bad when people like this don't appreciate the ASSET they have in an employee like you.  Well, just keep believing in yourself.  



I have to answer the questions you asked:  



Do admins really go to work every day and hide themselves?



NO!  I let my true colors shine through at work, and so far (six years into it) the future is bright, bright, bright!!  



Do I need to keep looking until I find my niche or do I need to change myself to fit in?



YES and NO!  Yes to keep looking...remember that your niche will find YOU if you keep your attitude on the right track.  But, NEVER NEVER change yourself to fit in!  You have to be you 100%.  



Are there creative industries where I'd be welcome? Or should I give up on being an admin and go and get trained to do something else?



Of course there are creative industries that welcome talented, creative, innovative, action-oriented, forward-thinking admins like you...I know, 'cuz I happen to work for one that appreciates me for who (and what) I am.  



Don't give up and keep believing in yourself.  Know that you will be OK.  One door shuts, but another (bigger and brighter) door opens.  It has happened to me, and it will happen for you, too.  



Take care............