I think you do have a case.
It is very good that you saw a doctor prior to being terminated. However, you should have asked for a claim form as well. Call your former employer, report your stress, request to fill out a claim form and ask to be sent to a doctor.
Get an attorney right away.
Likely yes if the stress is causing you to be disabled from doing your job. You should locate and consult with a workers compensation attorney right away to understand your rights.
Good luck to you.
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Based on the facts in your post, I don't really think you have a strong case. You can file a cumulative stress claim after 3 years of employment, but it won't get you very far. You will see a therapist for 6 months, claim to be permanently scarred by rude comments about your work quality, and possibly receive a nuisance settlement of a few thousand dollars. Even then, you will have a permanent record of being unable to work when someone criticizes you. This sounds like Personnel Action was the cause of your termination, which is an affirmative defense. That can defeat your claim even if you ARE upset and your feelings were bruised.
Looking for a new position is probably a better choice today, just as it would have been 6 months ago.
We offer general concepts, but you should give ALL your facts to a licensed Attorney in your state before you RELY upon any legal advice.
You may have a work comp case but it will likely lead to more detriment than good. You could also consult an employment lawyer to discuss a possibly wrongful termination case - although weak.