Due to G.E.R.D & the Ulcers in my fiance's digestive track, there are days where she would be stuck to a toilet or bucket because she can't stop vomiting, which causes her to call in from work. I've told her to take pictures of it so that way she has proof that it happened & regardless of how much proof we provide she would end up getting fired due to calling-in, so the most recent job she had we both agreed that she would just go into work for days she doesn't feel good & so that she would be paid for vomiting at work & to avoid getting a write-up, but it all ended in failure because she ended up getting fired over it.
You are really asking a legal question, not a tax question. We can only provide information about using the tax software here and help with tax questions.
For disabled adults:
There is an extra amount added to your standard deduction if you are legally blind. Your federal return does not provide any other credits or deductions for saying you are disabled.
For tax purposes, "disabled" means unable to perform gainful work due to a condition that is permanent or is expected to last at least one year. Because of the focus on gainful employment, many people with medically recognized disabilities are not actually considered "disabled" for tax purposes.
If you file as disabled, there are not really any significant additional tax benefits, other than the ability to take early withdrawals from certain retirement plans without the early withdrawal penalty. There is a small credit for being disabled that you probably don't qualify for if you work, and you can deduct his medical expenses, but you could do that already.
As noted, you may have more of a legal problem, if he wants to retire early on disability you may need to consult a lawyer who specializes in that. Also, the "permanent" part may be a problem for you since GERD can often be treated with drugs or surgery. There's not much you can do on your tax return without a medical certification that he is permanently disabled and unable to work, and even then, the tax benefits are minor.
@healingtrout hope she's seeing a doctor because GERD can lead to serious diseases.