Have you spoken to course tutors/welfare officers about your issues? Did you mention it during application? If you can prove you have a disability and/or mental health issue then they will be able to cut some slack and maybe assign someone to help you. If it's really bad you should maybe talk to a GP and find out about local mental health services.
But you do also need to tell yourself you've successfully completed a degree before, you'll be able to do it again. Don't aim for the highest marks, just for what you can physically and mentally do without pushing yourself too hard. I'm not a therapist so you do need to speak to a professional, but personally, a lot of my issues were caused not by my academic ability falling, but by setting myself goals I couldn't reach and bashing myself over the head when I didn't reach them.