Mags, you did well going to the shops. It's perfectly natural and expected to feel overwhelmed looking at all the christmas stuff, we are women, and what does christmas pose for us ? More work and stress, don't get me wrong I love it when it's here but the build up is busy, lots to remember etc. if you felt 100% , I'm sure you'd feel a bit stressed, if you are suffering from anxiety and depression it can feel overwhelming.
If you had for eg, glandular fever, christmas would be really difficult, so think of it like that. You'll have to delegate, let christmas come, do what you feel up to, and if you want to rest in your bedroom then do and don't beat yourself up about it.
If you have a good hubby, make some lists , ask for help and shop on line for groceries, presents etc. make it as easy as you possible can for yourself, and if you don't feel like doing something, don't do it, wait till you feel a bit better, which you WILL. The anxiety will wax and wane, pace yourself for now, and try to eat little and often, I promise you this helps x