I think most of us tend to become more easily upset as we age, and quite honestly, dear Biscuitmuncher everything does seem to be conspiring against you right now.
A 19 year old daughter not coming home for Christmas, and if I know that score, announcing the fact casually at the end of a phone call, or on her way out of the door, upsets mothers - take it from me, I know. I dissolved into tears when my 45 year old daughter annonced she and her son would not be coming for the 10 day stay in his summer holiday that was planned.
AND your daughter's rabbit is dying - and it is no consolation to know that as she is nineteen now, and got it while she was at school, that it has had a long and happy life.
Anyone who has had a pet, and if you read the pets thread you will see I am one of them knows that by now that rabbit is part of the family and it is DYING- make a big fuss of it, ease its passing and dig a grave in the garden while you cry, and sore knee or not, you will manage the task. The last cat's grave I dug, I dug with a sore shoulder and used a hand trowel more than the garden fork!
Next point: no-one on this earth can feel cheerful with a sore knee! So, I hope it gets better soon, and if it doesn't that you can get an appointment with your GP and get something done about that knee. You didn't say what is wrong with it, so I don't know whether you will need to bug your doctor until he/she does something useful, or whether a tube of Volteren oinment will do the trick - they make pills too, which are good, but I do not know if you can buy them in the UK.
And you are not alone, even although it feels like it - we are all here and know all about the days where everything just feels wrong, grey, depressing and boring and when it ALL hurts. So moan all you want - that is one of the good things about Gransnet - we all know what you are talking about.
Hope you feel better soon,