Hi OP, sorry to hear you are having such a rough time. I know it's hard but can you take one step at a time, maybe for now just focus on preparing as well as you can for the interview tomorrow and don't worry too much about what can/will happen if you get it?
If you are feeling really down it might be a good idea to seek some help from your GP regardless of the outcome?
If you do get the job, I think you'd have various options. You could get signed off for the duration of your notice period if you are not fit to be at work but I'd then expect this to be mentioned in your reference to new employer which might give them some cause for concern, and you might then have to explain the whole situation to them which could be a bit stressful in itself? But of course if you are not well enough to be at work then you have no choice.
You might find that once you know you are leaving the stress reduces a bit, how long is your notice period- many contracts/policies provide for a short notice period whilst you are on probation, sometimes as little as 1-2 weeks? For the people I manage if they are on notice periods of 4 weeks or less, I ask them to start handing over work pretty much as soon as they've handed their notice in, particularly complex things. So you may find your workload decreases and the pressure is off a bit fairly quickly?
Your current work may also be agreeable to you reducing your notice period a bit, again as a manager I am often OK with this as I don't want unhappy/disengaged people forced to be there. They may even (and I say may because some employers would never countenance this) agree to put you on gardening leave for some or all of your notice period. Or maybe you could use some annual leave if you are owed any to reduce your 'effective' notice period.
As a 'nuclear' option if they won't agree to reduce your notice in any way, you could just walk away from the job without serving your full contractual notice period. You would technically be in breach of contract but realistically there is little or no comeback an employer can exercise against an employee doing this, except mentioning it in any future reference. If you feel too stressed to go back to that job but feel able to start your new one then this could be not the worst thing in the world, although sounds like ideally you need a bit of a break to recover a bit and get yourself prepared for a new role?
But as I say, hang on in there, focus on the interview for now and take it from there. Good luck!