Your symptoms sound soo much like mine its spooky. I have breathing issues that go back about a year and a half . I was also diagnosed with complex /central sleep apnea the cause is yet unknown. I twitch constantly 24/7 all around the body but mostly around the legs and knees and like you I had massive fears of all this being the start of some sort of respiratory onset ALS .
Now I want you to listen to this next bit ...
The chances of this being ALS are highly unlikely .. it could be down to metabolic reasons ,bad diet or just plain old stress ( I know how you dont wanna hear that but its true) ... Or lots of other things that are treatable . I know how easy it is to not look any further than ALS when you have this going on but I have had it for 18 months and breathing issues aside I am pretty fine still working as a nightclub bouncer.
If you wanna talk then pm me and I will be there , Good luck and God bless .... alex