I can relate to this feeling, Skydancer. I agree with the suggestions that you talk to your GP, or find a counsellor. I'm wondering if you are feeling as if you are of no use to anyone any more; that can bring you down a lot. Remember YOU STILL MATTER AND YOU STILL HAVE VALUE, even if you children and grandchildren no more need the same kind of care.
Everyone's different, but I have found recently that I've become a bit more 'okay' about myself, and all I've done over the last months is so write in a notebook every day three things that I am grateful for and three things I've achieved the day before. Often they are tiny things, but sitting with a pen and notebook and trying to think of things helps (I think!). Also I am listening to a short guided meditation each morning.
Basically I wasn't expecting much to improve, but I'm delighted to say it has! And at no cost (free app Insight Timer for the meditations).
Sending a BIG hug and 