You know it is all going to be okay don't you? It is still (just) November. There is plenty of time to get everything done, as long as you do a little bit every day - hey?\
Your task for today is: write 5 Christmas cards.
That is all - just 5 (more if you really feel like it). The act of writing the cards will make you feel calmer, in control and organised.
If you are not sending any paper cards at all this year, spend 10 minutes looking for an e-card design that you like, or composing your Christmas email for all and sundry.
These things don't take a long time - we build them up into an insurmountable problem, we forget how to breathe and we panic.
Go on, just write 5 cards today. You'll feel better for it.