When I started twitching in december, my Doctor wondered if it might be due to over-use of my Ventolin (Albuterol) inhaler. Apparently, a certain chemical imbalance (due to overuse of inhalers) can be one possible cause of twitching. She sent me for a blood test, but that was not the answer.
She then suggested that since my asthma (which I have suffered from since age 5) was not serious, that I might be over-using my inhaler due to anxiety!
I tend to agree with her. It all "fits". Asthma is triggered by anxiety and I think the twitches are anxiety related too.