Just figured I'd mention that sleep paralysis is there for a purpose. From a non paranormal perspective, it's there to protect ourselves from injuring ourselves. The opposite of sleep paralysis would be sleep walking and that has caused many disasters in the past.
You only experience the paralysis part when the mind has woken up before the body, in which case shouting out something like that could have a shock affect on your body essentially willing yourself to get up. Dark figures in the corner of the eyes may just be tricks playing on your mind, which is understandable since paralysis usually induces fear within an individual.
If this has all been mentioned before, err please disregard this post.