Depending on the disease you're dealing with, end of life symptoms can vary, your physician should be your first source of information about your particular situation.
I would love
to help you with more information here however, without knowing your specific circumstances, I may only overwhelm you with information you don't need.
There is a fabulous book that I give to all of my patient's loved-ones called "Gone From My Sight" by Barbara Karnes - you can order it online by doing an internet search. The book is a small pamphlet that discusses the signs and symptoms of approaching death from the last months of life to the last hours. It is a very easy read and I've only had rave reviews from those who have read it.
You are doing the right thing by looking for answers. Best of luck.