I've just read this thread, and it definitely resonates. My heart goes out to all of you in a similar situation, now or past.
My background: my 73 year old mother was hospitalized in January 2015 after being found outside in the cold, no coat, wandering, disoriented, hallucinating, and injured. She was sectioned/spent 2 weeks in the Geriatric Psychiatric ward (UK/US terminology), diagnosed with dementia, assessed and determined to be unable to live alone and require 24-hour care, and discharged to the care home, which is about 10 miles from where I live.
Previously, she had been living alone with no services or assistance, 100 miles (a 1.5-2 hour journey by car) from me. Over the past several years she'd suffered a variety of minor health ills and I was making that trip anywhere from once a month to once a week. Now I know it was the dementia (Alzheimer's type) that was causing all the weird behaviour and problems taking her medications and her weight loss and refusal to eat or bathe, refusal to go to the doctor, refusal to let me see most of her house, et cetera. A lot of you have been there and know what I mean.
So on those trips, which were admittedly nothing like as long as the journey the OP is describing, I often found myself sad, unhappy, depressed, dreading it, angry, you name it. I would be like that before and after a trip; I could deal with her while I was with her, but then might be upset for days.
Now I visit her in the care home about once a week or every two weeks and often cry or yell or just plain get upset afterwards.
Here are things I tried and did that worked for me:
When I used to take the longer journey to see her, I would try to schedule something pleasant for myself to do on the same trip (see a friend or favorite aunt who lived in the same city were the best options) so that the trip wasn't just about seeing my mother and taking her to the doctor, et cetera. On the drive down I would make sure I had something with me in the car I wanted to listen to (and I would take my husband's car, which has a CD player and cruise control--my car does not), whether it was a radio programme, an audio book, or music. On the way home, I would do the same, OR I would arrange a phone call with a friend to distract me. Before I would drive home I would make sure I had eaten and/or had a snack with me, and sometimes would go to the store and buy a new album to listen to (OK, only twice, but it was a good idea).
I foolishly thought that now she lives nearer to me, I wouldn't get so upset after visiting. Well, I learned my lesson on that one. If it's a bad dementia day, it's upsetting. If it's one of her more lucid days, it's just as upsetting in a different way. She is nicer to me now, but is currently a bit agitated about Christmas and not being "home." I dread, dread, dread the comments about "home."
I visit her with my husband and what works best for me (after getting to the car and yelling and/or crying and/or hitting things) is for the two of us to go for a walk somewhere, preferably a nice park, but anywhere will do. Being outside and moving helps me.
I also like to have a plan of what we will do, before we go to see my mother. This gives me the illusion of control over my life (because with dementia, there is no control) and also I know what to expect and if I've agreed to it in advance, I can't back out and go home and get in bed and pull the covers over my head, which is often all I want to do after seeing my mother.
Then if my husband and I do some normal, boring, domestic things (run errands, go home and cook dinner) I am usually okay, although I'm often upset the next day.
Other things that have helped me, in no particular order:
-chocolate
-wine
-TP (the only place I feel really safe to talk about everything)
-I've tried several support groups and one in particular is good
-talking to the approximately three friends who understand and have not disappeared, although I try not to do this too much
-my therapist (cognitive-behavioural therapy as mentioned above)
-my massage therapist, who has helped with back pain and headaches from muscle tension and stress
-my mailman, when I catch him, whose father had Alzheimer's and who always has a kind word for me
-stupid, mindless television
-exercise, any sort
-being sociable, especially when I don't feel like it
-being around small children
-doing any sort of volunteer work/nice things for other people
-cooking, when I have the time and energy
What would help most? More time and energy!
While it was a massive relief, especially at first, to have my mother somewhere SAFE (no more nightmares about her hurting herself or someone else), I am finding, as time passes, that the paperwork/administrative side of things is incredibly horrible. I expect others know what I mean.
I know that washed out feeling all too well.
Wishing you all the best Christmas possible.