Do you pay for short term / long term disability (STD / LTD) in your companies benefits package or individually (maybe packaged with life insurance)? If so, you should:
See your doctor and have it documented that your physical and mental health is being damaged. Don't lie. Just tell him what you told us. Get him to write that in his notes. The more visits, the better, but one should be enough to start the process.
Start seeing a therapist/psychologist (not an MD Doctor) for your own well being, but also, more documentation. If you have benefits this is likely billable to that.
Approach your companies HR or your manager and tell them you would like to start the Short Term disability process. At this point, your work is taken out of the loop, and you will communicate with the insurance companies rep. This person is not really on your side. Only speak factually to them. They will provide you some forms to sign and get sign by your doctor. Get a copy of your doctors notes (request them from their office). Package everything together and submit to insurance.
If you are not approved on this submission you can appeal. You may have had more doctors visits or therapist visits. You can ask your therapist to write a letter for this process.
Consider hiring a lawyer (its cheap in the long run, expect $1000-3000) to help you navigate this process so you can focus on your mental health and recovery.
Decide if you want to return to this job or quit. If you take STD or LTD you do not have to return to your employer.
Source: Went through what you did and went through all the above.