Bipolar Depression

I need some advice if anyone has any. My husband whom I am separated from is in a depression mode. This happens periodically, most of the time he is more manic. When depressed he tends to go to bed for many, many hours. Won't return phone calls or answer the door if someone goes to check. I am concerned for is well-being, but I don't know how to react to this, I have never yet worked out how to handle the depression. Is it best to leave him alone, or is it best to try to get him up and about, even though it is very hard to do, especially living apart from him? Anyone know? Thanks everyone.