valid question, and we will all answer differently.
firstly, I know I am a CALS, but it is something I have discussed at length with my husband.
Usually the build up of CO2 causes drowsiness, so if they give you extra oxygen and morphine you shouldn't have too much air hunger and distress.
Elaine is so right about starting early, taking tiny frequent amounts of morphine or similar. The idea is to PREVENT high pain or panic, not have to climb over it once it sets in. You are more lucid and in control this way too.
The decision of where to die is very personal for both the PALS and CALS.
I look at it this way - I WANT my husband to die here at home. He couldn't quite understand it at first but for me it means he can have his final days with me and we can do it our way. I don't want to sit in a hospital anywhere, and I want to do whatever I feel when it happens. I can keep him here with me as long or short a time as I want before I have to call anyone in. I like this idea, and I know that I won't see any room in the house as the one he 'died' in, I will see him having as much dignity and love as possible and always be grateful I could provide that. I personally would have no problem giving him a final dose of anything.
However, having said all of that, this is how it is for ME, and I wouldn't tell anyone they should do it my way, or differently to how they are. Some people would genuinely be terrified of being alone with their PALS when they gain their wings. In that case, I would not want any CALS to go through that.
Forester, many PALS don't even realise the end is upon them and simply don't wake one morning. I constantly pray my husband will go that way and I make sure that I enjoy every evening with him and go to sleep with an air of love in the house.