First and foremost - no, you most definitely have not let your mum down. Eight years is a long haul when caring for a loved one with dementia - and it definitely doesn't get easier as time goes by.
On top of that you are grieving for the loss of your beloved brother who has played such a part in keeping you positive. No wonder you are struggling and frightened right now.
For many of us, no matter how well we have been coping, a sudden change in health or circumstances (or both) can come along and make us realise that we have come as far as we can on our own, and that it is time to make arrangements that are in our loved one's best interests.
You have made that step magnificently well. Your mother is in a good nursing home and I am sure that, in time, you will find it easier to visit her. It is just all very new and strange right now and needs time for adjustment.
I am going through something similar with my husband. His mental and physical health went downhill quite fast early in January and he has been in an NHS dementia unit since February. We are currently going through the process of sorting out a nursing home.
It hurts, I know it hurts, and it can be scary. I completely understand the staying in bed reference - I did it myself a few weeks ago. I knew it would achieve nothing, the situation would not change and all the practical stuff would still be there when I emerged from under the duvet - but everything was closing in on me, and for that day or two I needed to shut everything out for my own health as it was all becoming quite overwhelming.
While I was under the duvet, unbothered by external interruptions, I found the time and space to acknowledge that things were beyond my control and that I would either have to go with the flow as best I could or become ill. I found a new resolve to face the quickly changing situation and I emerged to fight another day.
When you have cared so long and carefully for someone like we have it is hard to let go of the reins. It is hard to realise that once where we knew everything there was to know and understand about that person - suddenly there are things that others know that we do not.
The shock of not knowing something hit me a couple of weeks ago when my husband had to have an emergency operation. I felt useless not being able to tell them basic stuff like when he had last eaten or drunk something, when he'd last had a bowel motion, whether he had loose stools etc. I knew his medications but not the current doses (they keep getting tweaked) - nor did I know at what times of day they are administered. This was all information that I could previously have reeled off without a second thought.
However, despite these gaps, my role and knowledge in my husband's care is not diminished, just slightly changed. I have known him 40 years and will have been married to him 36 years come December, so there is so much I know about him which will be vital in making sure his needs and preferences are met going forward.
I also understand your concerns about weight loss. My husband, who had a very healthy appetite, has been losing weight since January because he eats less and less, as do several other patients in his unit. It seems to be part and parcel of the progression of the disease in the later stages. There have always been general requests for me to help encourage him to eat and drink when I visit, as is the case with other patients being visited by their family.
However, it was only a couple of weeks ago that I was directly approached with more urgency and updated on a significant weight loss over a nine week period. I assume that I was directly informed at that point because he now scores 2 on the Malnutrition Universal Screening Tool (MUST) and is at high risk of malnutrition. Up until that point I had known there were weight issues but the severity was not flagged up with me until he reached that new level.
Like you, I often find my loved one asleep whenever I visit - I go at different times and it makes little difference. I also know that he often has his eyes closed but is actually awake. Sometimes I just hold his hand, sometimes I chat a little, sometimes I play his favourite music on a portable CD player. I just let him rest and enjoy the moments (the occasional hand squeeze, smile or brief glance) as best I can. In some small way we are still connecting and it is lovely.
I am gradually getting over the guilty feeling that I could have done more. If anything there are definite benefits to no longer being the hands on carer and I am sure you will eventually find the same with your mum. It allows us as carers to have a more peaceful time and quality time with our loved ones. I am actually happier to find myself once more able to think of myself as a wife again rather than a carer. But I am a wife who still has much to offer in making sure my husband's care and well-being is the best it can be. Its just that I no longer have to go it alone.
I hope that you too will find peace and calm as you let go a little bit and that, once all the practical stuff is sorted, you will relax back into the mother and daughter role, knowing that you have, and still are, making sure mum's best interests are met.