Anger isnt strange -you had such lovely plans. I have two daughters, one on the other side of the world,but the other still in the UK, and that is the same idea we are having too, me moving closer too her.
My mum had cancer and i cared for her as long as i could.But we lived in a remote place, it was a really bad winter and there was a risk that if she needed extra medical care they wouldnt be able to get too us, so she made the decision to go into hospital for a while and didnt come out.
On the day she died more snow was imminent and she sent us home to avoid it,so i also wasnt there when she died,no-one was, because the end came so quickly. It left guilt anger and a lot of unanswered questions about her care, but i had to accept that they would never be answered. And just as you went on holiday, i went home so i completely understand you feel bad about it. The truth is we only have hindsight we cant see the future.,Your mum would have approved of your holiday and it was her choice to stay at home,just as it was my mums to go into hospital.
Even though it hurts and we are surounded by all those "what if" questions we have to respect their decisions esepcially when, as you say, she was very independant.
IF you are having actual panic attacks they will pass,i had them when my husband died -which was what brought me here,but one solution that helped a bit was to carry something solid and real in my pocket -in my case it was a quartz crystal he gave me -but it could be anything -perhaps something of your mums, or a pebble off a beach that you went too as a child.Hold it tight in your hand and focus on breathing more slowly.
It is a difficult time to be thinking about the big decisions such as moving -but what will happen too your mums house seems like a place to start. Moving into it might be one option that can be consoling ,but moving opposite and seeing some-one else living in it might be too painful.When my mum stayed at ours she like to watch the birds outside so i set up feeders etc where she could see them from the window -after she died i created a corner of the garden as a memorial with all the feeders, water feature and favourite plants,-i have moved since then and brough it all with me and will do so when i move again,so it is possible to have that connection wherever you live.
Please dont feel you need to apologise for long posts,thats what we are here for and writing, i find, helps.