I am in a similar position as you. I have a medical issue and I was fired in August 2018. Differences being:

- I intentionally got myself fired so I could get an extra $25k in salary/severance/unemployment.

- It was my first job out of college.

- I have positive references I can give. (my manager sucked, other people were cool)

- Medical issue is physical and not mental. (herniated disc / sciatica).

Here is my advice:

- Practice interviewing at a bunch of no-name companies you don't care about. I practiced at a dozen or so startups, got rejected by half of them and learned the red flags. Now I'm at the onsite stage at Google / Facebook, both asked about previous employment history, which I talked about, and everything worked out ok because I practiced.

- DO NOT MENTION, OR INSINUATE, YOU WERE FIRED. And don't lie. If you imply that you were fired, nobody will give you a chance. This sounds like a death sentence, but thankfully interviewers don't probe into it too much if you tell the right story in the right way. Find a good narrative and build on it like you would an essay. Practice this. Over and over and over and over again. It's hard to get right, but once you do, it becomes a non-issue.

- I try to avoid saying negative stuff about my last job. It's about 50/50, some hiring managers see it as a red flag and others sympathize. It's best to come up with and practice a few neutral stories to tell them

- Nobody cares about a 6-month employment gap. I know plenty of people that take more than a year off. If anyone asks just say you were focusing on your health, family, hobbies, whatever.

- See as many practitioners as you possibly can about your medical issue. Good ones are hard to find. It took me 20 tries (and $5k down the toilet) before I found someone who could treat me.

- I should have put this behind me way sooner. Moving to a different city helped me a ton. I'd recommend getting an Airbnb in Lake Tahoe or Hawaii if you can afford it.

Good luck.