I just read answer to part of my own question but I figured Id share...accordingly to the document on MGFA website titled "MG A manual for the health care provider" page 51 section 3.5 reads
"One distinctive characteristc of the MG patient during evaluation of respiratory strength is that blood gas or oxygen saturation percentage is not a good indicator of respiratory strength. MG does not interfere with gas exchange itself but the capacity of the chest muscles to support respiration."

sooooo how do we know if trouble breathing is crisis and need ER or if need to just lay down and be cakm?