Imagine waking up one morning only to discover that you're trapped in your body! You open your eyes to frantically discover that you're still alive. You role your eyes down to look towards your legs and they're still there, but unable to move. You're completely paralyzed, can't speak, can't yell for help...all you can do is move your eyes up and down. The only movement you have left in your body consists of vertical movements of the eyes because the only 2 nerves spared in this state are the oculomotor and trochlear nerves. You can hear yourself think, you can hear people around you speak, you can even understand what they're saying, but you're trapped! A prisoner of your own body. You can't express to anyone around you that you're scared to death or want to cry.
This is what is experienced by thousands of unlucky people with "Locked in syndrome" or cerebromedullospinal disconnection. It is caused by a lesion at the base of the pons such as an infarct of the basilar artery.
Corticospinal tracts are lost, meaning you have no movement in your body.
Corticobulbar tracts are lost, meaning that you have no movement in your face and can't speak. All you have are the up and down movements that you can perform using the oculomotor nerve.
This is the scariest disease to me. I would probably prefer to have any other disease than this.