On the uni work, there is some advice I can offer.
First, you are by no means the first student in this situation. So don't feel for a second that you are entering new waters.
Having been absent at the first attempt, I'm assuming you have mitigating circumstances or similar? For most unis, this means that the resit is actually the first attempt. But, crucially, if you are still suffering from the circumstances (and it sounds like you do) you should be able to apply again. Should you do this you would be able to take these assessments in the next academic year. If you didn't get an MC first time around, you still can for the resit.
The pros of this are that it gives you time and space to work on your own issues, then tackle these assessments at a time when you are better able to. If this is ongoing, you could also apply for a temporary suspension of studies which effectively pauses your studies until you are better.
The cons: your graduation is pushed back a year, and some folk find that hard to take, and worry about what to say to people.
It's good you are in touch with the counseling service. Also talk to your personal tutor/academic mentor (whatever the term is at your uni).
On the dissertation, it's just like eating an elephant. One bite at a time. Don't concern yourself with the size of the finished product.
Drop me a PM if you want to discuss any of this further. I know this is more practical advice than emotional support, but I hope it helps.