I, too, tried to apply for SSDI while I was still active due to depression. I was denied because the person who applies has to earn below a certain percentage equal to the civilian equivalent of your military job (at least this is how it was explained to me). Even though I was working part time when I applied, I still "earned" too much. However, I applied again right when I went on terminal leave, and was approved. But this took a few months, and I had to wait, I think, 6 months to start collecting. It is a long and difficult process. Each person is different, but that was my experience.
Have you went to DTAP, yet? There's usually a representative from SSA who speaks. You may reach out to them and start the process.
But like
@chaplaincharlie said, it doesn't hurt to apply. You won't know until you try.