The NEC has no provisions to adapt for any special needs of the end user, and it is not subject to the requirements of the ADA. No you cannot put a panel sideways. Well, there is another recent thread that discusses this same question, and there are some members who say that you can. But if you do, then half of the breakers cannot be used. The problem is that a breaker with a handle that moves up and down must be installed such that "up" is the "on" position. Reference 240.33 and 240.81.