I used to be on bi pap before the vent and can certainly understand how you are feeling regarding getting used to the thing. I think the hardest part was trying to breathe with it, I found that initially I fought it and was counter productive. It does take time to get used to as well, so if this is very new, then it might take a bit to get the hang of it...it feels very foreign at first. Another thing, is your mask giving you problems? Does it leak or just not feel right? There are different methods of delivery, such as nasal pillows, which kind of looks like a big version of a nasal cannula. I used that as well as the traditional mask alternating them. There are also several different types of masks on the market, sometimes you have to try different ones before you find one that fits you just right.
I was on bi pap nearly 24/7 nearing the vent, so rotating the two became very important if I wanted to remain comfortable as you can experience skin break downs around the seals of the mask, as well as irritation of the nares from the nasal pillows.
I think it is a good idea that you try the chin strap to prevent mouth breathing, that may be part of why you aren't dealing with it well...all of that support that the bipap is giving you is leaking right out of your mouth instead of going into your lungs which might make you feel like you are suffocating. I had a chin strap as well and found it helpful, I too was a mouth breather and felt better once the machine was delivering air to the right place.
Lastly, if you aren't getting humidity, you should. The air can be very drying, you would be surprised how much easier it is to tolerate when there is added humidity.
I hope this helps and keep at it...once you get used to it, you will feel much better and have more energy during the day as your lungs are getting the rest they need.
Good luck...Jenn <img src="i/expressions/face-icon-small-smile.gif" border="0">