You sound like you're depressed, flip, down in the dumps, with a lot on your plate at the moment - and lots facing you with the move and the dark nights, and Christmas.
I don't think you have depression, which is a clinical condition, but I think you have a lot on your back - but you have done the right first thing in recognising that you are down. Clinical depression has a nasty habit of sneaking up you and you don't realise that you are there 'til you're in it.
I find that when things get me down like this - and it does, heavy workloads at work, home demands, long office journeys - I make lists of the things I need to do. Yes it can be daunting but at least then you can see what you are facing, and you can get satisfaction from starting to cross them off.
There is something to remember here - you have to differentiate between the things you can do something about, and the things you can't, that will happen with or without your action. Your sister's situation is very worrying for you all, but she is doing the right thing in having the op, but you can't do anything about that - that's out of your hands. Try to differentiate between things you can affect, and things you can't - that helped me, to see the things which are getting you down that I could take action on, and the ones I just had to wait and see. Your sis is one, and the dark nights is another - you can't influence those.
Try to focus on good things - your new job, your sister coming to stay after her op - get things ready for her coming to you, get yourself in order for the new job, and hopefully the other things will come into perspective. Make sure you are sleeping enough and at the right times too - daytime hiberation is great, but it's a way of shutting stuff out, and you need not to do that.
I hope this helps - I know where you (although under different circumstances). Keep talking to us, too!