I am planning to ask for an extended break from my employer. They however might ask for a letter from a doctor explaining why I need an extended break.

What will a doctor write in such a letter? Has anyone had experience with this?

I am not asking about using FMLA or anything. I knew a colleague in the past who just went away for 3 months for a medical issue and he didn't apply through FMLA. He just said he showed a doctor letter, but he had a real neurological problem.