I like the idea of telling them you were a care-giver for someone in your family. It's sort of bending the truth a little, but if it ever comes up, that's better than an outright lie (I spent 3 years in the Yukon wrestling polar bears, etc.). I think someone said this already, but they aren't allowed to ask you who or why.

Good for you on going to school to better yourself. For someone with a serious mental health problem, that's something you can be proud of. Keep up the good work. Stay focused. I have faith in you.