Asking questions in a safe time and place is fine. Just remember that it is not your job to test someone's disability, in order to make sure that it is real. Without the correct qualifications, you have no business telling people that their disabilities aren't real if because YOU have no experience with it. In the same way that world hunger does't stop being real, just because you have always been able to make a sandwich whenever you wanted one - a person can still be disabled, even if you can't see it. Looking "normal" doesn't play a factor. Try to be tactful and polite. Don't expect information that you wouldn't be willing to share and don't blame somebody you've never met before, for the way that YOU decide to treat them.