I have had your exact symptom of waking up gasping for air, and the rest of my body is freaking out, too.

I was diagnosed with MS-related central sleep apnea. The more common sleep apnea, obstructive sleep apnea, is when you stop breathing because of an obstruction in your airway. Central sleep apnea is the result of having your brain fail to signal your body to breathe, and in MS it is because of damage to the portion of your brain that controls that sort of thing.

As a result I am now on O2 at night. It hasn't happened to me since I started the O2.