Why has my Mum's health taken a very sudden bad turn?

It's as though it happened overnight. Please someone guide me on this. I'm so upset well my mum has had a lot of health problems over the past few years.she had serious heart problems ,shes had a heart attack and had a stent put in.then 3 weeks after a heart attack,my,mum had a stroke that left her left arm paralized.she was so ill at first I didn't know what to expect but she did recover and she was eventually allowed home .she could walk a little at home with an aide of a stick.but still her arm remained paralysed and of no use.so basically it just hangs heavily by her side.after a few months though she was living very independently,and could cook and dress herself.it took over a year for my mum to get back to her ususal self and although she had a problem with swallowing some foods.she walways looked so fit and so well.i see my mum twicw a week I do her shopping for her and the house work,then one week I noticed how much weight she had lost ,how suddenly it seemed to happen.i noticed she was out of breath and she was struggling to catch a breath.so the doctor came out and took blood tests and checked everything out and he said that there everthing seemed normal her heart rate and her chest and a;; his other tests said she was fine.a week later I spoke to the doctor saying I was concerned about her as she didn't seem to be eating much,she had lost weight etc.
then my mum had said she had a severe bout of diarrhea which she couldn't hold back until she got to the toilet,she had tablets of the doctor but after lots of tests and a lot more spells of diarrhea still the doctors couldn't find anything wrong.then I again had the doc out and he took blood tests it .that's when it resulted in my mum being found anaemic ,however it wasn't through lack of iron as she had plenty of that in her.however my mum thatn admitted that she had diarrhea for a while and that it put her of food,so much that she didn't even feel hungry or want to eat.she became so frail looking ,then the doctor gave her complan.but no help for anaemia ,after complan my mum got stronger mentally but found she was weak and exhausted.then suddenly my mum wanted to eat and I made her chicken soups etc,then I made her a sausage sandwich and she loved it then an hour later my mum had diarrhea very badly.my mum has never been depressed but since diarrhea my mum has been complaining of depression and of feeling lost and lonely,she is sp frail and weak and out of breath ,her memory isn't good and some things she says are so out of character,ive got 3 teenage children and I have no car and I live about an hours bus ride away from her.i suffer with severe depression.but I have been constant at my mums for 3 years now.catching a bus down and my partner is there fwhen my kids get home.ive got 2 brothers who live near by and a sister who lives across the road from my mum.they dint help much before but now they do pop in and out to see her.i do 3 days a week and I feel so guilty at this because I want to do more just ive gotto see to my house work my kids like me being there when they get home.plus I need some time to myself just so I can keep my depression intact .just I feel so bad about my mum and she has said she misses me but on the days im not there my sister calls to see her in the morning and at night and my brother pops in too.just I feel as though im not doing enough but on a person level I feel as though it sometimes drains me,i love my mum and I do all I can for her,i know she would rather me be there than anyone else and shes always asking me to live with her,but I cant my kids are settled and overall its impossible .do I accept my mums at the stage where her being frail will happen,my mum is 78 by the way.i just need some advice on how to cope with this. thanks