The first thing I thought of was this: (Loud sound warning) Be sure to do a thorough job researching precisely what it feels like to have those disorders, and get first-hand accounts if possible. I'm sure the last thing you'd want to do is offend someone with one of those disorders by misrepresenting it. Also, start small, by picking one disorder and sticking with it until it's perfect. I'd like to see the PTSD one, myself. I think that option might be able to deliver the most realistic experience for players, while making them feel like one with PTSD feels, without necessarily just getting frustrated by the game. I think that would be the easiest one for players to empathize with.
Yep, definitely be smarter to start smaller. PTSD would be a safe thing to focus on to start, and I agree with you that it'd be the most familiar to the widest array of users. And yes, as I mentioned in another comment, I'd be very, very careful, and would seek the input of people with the mental differences in question. I don't want to be me telling what it's like for everyone with, say, OCD. I want instead for these people to tell me directly. I'd seen that video before, and yes, definitely a good one, thanks for reminding me of it. If you're interested, here's another one, with a different style, this video being the catalyst that made me think about this worldbuilding idea, as I liked how the experience was portrayed, and it seemed something that'd be easy to implement in a game: