I have uncomfortable, occasionally painful twitching and spasmic feelings around navel, left ab, and chest. started while playing sax 2 mo.s ago. ?

Posible subclinical: periumbilical hernia versus abdominal muscular strain- both easily checked by your physician.

Ok: It sounds as if by starting to play the sax, you have in some way irritated or caused a sprain of some muscle groups. see your dr. and get a good clinical exam to get a definitive diagnosis so any treatment can start. Best wishes.