Is it considered disability discrimination if I was fired because I took a sick day because my blood sugars were all over the place?
No. This is not disability discrimination. If your blood sugars were bad enough ti call off, they were bad enough to need a Drs note. I have a feeling youve called off MULTIPLE times now, and needed the note to make it an excused absense. If your diabetes is poorly managed, ask about an intermittent medical leave.
The laws about disabilities only say that an employer has to make "reasonable accommodations"- like wheel chair ramps, etc. They are not required to employ someone who can't do the job. Now, how upset they'll be over this one absence depends on how dependable you've been in the past and how valuable you are to them.
If you're having trouble managing your blood sugars to the point where you have to call in sick, you need to ask your doctor about referring you to a Diabetic Educator. A Diabetic Educator will teach you how to effectively manage your blood sugars through diet and exercise and how to manage your diabetes when you're sick as well.
Pascal the Gambler
Nope. They are firing you for not coming to work, not for having your disability.