I'm sorry for your loss @StMarieforme
Yes, it's natural to feel this way, a natural reaction to the grief you are feeling.
I'm presuming you would still be troubled by the problems you have had for a long time, but your dearly loved friend gave you strength to cope with them, over many many years, by being a good listener if nothing else.
She was always there to listen and you listened to her and together you could commiserate and you now feel very alone in all of this with no one you wish to share your troubles with.
You said you were having a better time of it lately, and now, when you hit a bad patch, there's no one to help make it seem not so bad, no one to confide in.
That's very hard, I know, when you feel alone with no one to turn to.
I believe you're feeling so down you can't see the end, but things will get better, they have before, but you'll have to draw on your own strength, and imagine what your friend might have said to you to make it seem bearable.
I hope you have better news about your own health, all the best xx