Stella:
Yes, I totally agree with above 's answer, as my husband is in the same boat as you, and even if he takes a np, he has to use the bipap. So, I believe it will sith much less work on the lung/heart by using it, versus the opposite.
My parayers are with you and your family, as I do know how difficult this can be for you.
You really should wear it every night, for both physiologic reasons, including high blood pressure in the pulmonary arteries, and to ease your breathing. It can make a significant difference in the quality of your sleep and that, in turn, can be a major determinant of how you feel the next day. There are no adverse effects from using it faithfully every night.