Job resignation - Breaking notice period

See a doctor a

(Oops)
See a doctor and get yourself signed off sick for stress/depression/harassment/whatever. That's clearly what the problem is, so don't feel guilty about it.

Have you asked whether they would be happy to let you go without working out your full notice period? If they will, your problem is solved; if they will not, you know that you are going to have difficulties.
The problem is that there are many things that they CAN do but you have no idea what they WILL do. For sure they will not pay you and they may refuse to give you a reference which is likely to cause problems with any future employer.
They can sue you for breach of contract and for the costs of replacing you at short notice though that is extremely unlikely; similarly they can insist that you work out your notice in full and that does NOT include holidays or time off through sickness but, again, that is not likely to happen.
The bottom line is that, if they refuse to let you go without working out your full notice period, they COULD make life very uncomfortable for you.

Actually - getting yourself signed off sick is a very bad idea as it will extend your notice period for every day that you're off sick.

If you just stop coming to work that's even worse, as they will just fire you for "faute grave" and you'll have that on your file.

What KASSEISTAMPER says makes much more sense, you should speak to your company and ask if you can leave sooner / tell them you want to leave now. Most employers, unless they're being deliberately malicious, will come to an agreement with you. i.e. you leave earlier, they don't pay you.

Try your very best to tolerate it and be brave and strong. It is not forever. Stay positive.

Try as well to balance out each bad day with something nice (helping out, yoga classes, gym, running, meeting +ve friends) etc that will help getting you to the finish line much more bearable and easier.