You should find a new doctor or ask why your doctor refuses to fill out FMLA forms if you have a legitimate medical reason for missing work and the FMLA forms are required.
This is not an employment question. It is an issue between you and your doctor. If the doctor will not certify that you need additional time off, and you believe you need more time off, you need to either convince your doctor to change his or her mind, or find another doctor, or go back to work as he or she instructs, or quit at your own peril.
It is not unlawful for your employer to require a doctor's certification of need for FMLA leave. Absent such a certification, it is not unlawful for your employer to expect you will return to work as the doctor has indicated you can.
I am sorry to hear about your situation. However, apparently your doctor is not hearing what you are saying, or is ignoring it, or believes you are capable of working through it.
Good luck to you.
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I agree with my colleagues but will add that there is no formal means required to notify your doctor you have a serious illness and cannot work for FMLA purposes. If you have provided your employer with a doctor's note that you are unable to work until December 1, due to a serious illness, that should be sufficient for your employer. If they do not believe your doctor, they have the option of requiring that you see a doctor of their choice, at their expense. If they give you a hard time about this, seek the assistance of an employment law attorney in your area.
They say you get what you pay for, and this response is free, so take it for what it is worth. This is my opinion based on very limited information. My opinion should not be taken as legal advice. For true advice, we would require a confidential consultation where I would ask you questions and get your complete story. This is a public forum, so remember, nothing here is confidential. Nor am I your attorney. I do not know who you are and you have not hired me to provide any legal service. To do so would require us to meet and sign written retainer agreement. My responses are intended for general information only.
You can return to the ER since they are familiar with your symptoms and request more help. If you have been bedridden for that long make sure they know that. Good luck. You have received excellent suggestions from my colleagues on this site.
Not legal advice / No lawyer/client relationship.