I have a newish Dreamstation auto CPAP. And flying DL on C+, thus fairly upright all night in a TATL. Do I need a doctor's letter at all? Will I have issues from TSA? I have GE, if that matters. Also, to add, I will also carry medically necessary 4-6 11oz cartons of Premier Protein drink as I am recovering from gastric bypass surgery. I supplement my protein intake as these drinks contain 30g of protein. I'll be in London for a week and won't have access to a blender; thus I am schlepping this in my carryon. I'm not bringing checkin luggage. I will obtain a doctor's letter for the protein shakes. It is my understanding I will be more than thoroughly screened because of the drinks. Did I say this is medically necessary?