Myasthenia Gravis Support Group
Myasthenia gravis (MG) is a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. Although myasthenia gravis may affect any voluntary muscle, muscles that control eye and eyelid movement, facial expression, and...
This was taken from one study from this website as an example
http://www.biomedcentral.com/1471-2474/5/42
During pregnancy 9 patients (50%) did not change the clinical status compared with before pregnancy, 2 (11%) had improvement and 7 (39%) had worsening of the MG. Pregnancy duration was 37.5 3.0 weeks (range 2941 weeks).
There are many factors that can trigger episodes of weakness in myasthenics, including other illnesses (e.g. viral respiratory infections), drugs that affect the neuromuscular junction, hot weather, pregnancy, and emotional upset. The undiagnosed myasthenic might not connect the various symptoms to one condition. It should be noted that pregnancy can worsten, improve or have no effect on the condition - that is, a woman will not know how pregnancy will affect her condition until she is actually pregnant.
This is from this website:
http://www.myasthenia.org.au/html/symptoms.htm
I agree with Elinora and unsure81 that breathing issues create anxiety because you don't know if you will get enough air, and, in my case, anxiety about having an "attack"in public.