I don't recall any of the warning signs specifically prohibiting diabetics from riding.
Since I am a person with an anxiety based mental illness, when I see "nervous conditions" mentioned on a ride I've never ridden I always ask a CM. Is it loud, fast, spinning, dark, closed in, stuffy, gory images... what is likely to bother those with "nervous conditions"?
While spinning, stuffy and unexpected loudness could send me to first aid, I love most of the wilder Disney rides. For someone else it may be dark and gory which does them in.
If you have any questions about a ride, ask a cast member. They explained to me that Star Tours is actually a motion simulator which never moves more than a few feet in any direction and I have been able to enjoy it ever since. On Soarin over California, I was shown to the seat on the far end of the bottom row, where I could fix my vision on the side wall if I got scared. The 3rd time I rode, I chose the center seat on the top row and kept my eyes open.
For me, Disney has been a place to start to conquer some real world fears.
