Sleep patterns in animals differ from those found in humans. People tend to sleep deeply and often, but for animals they sleep quite differently.
It is true that blacks and predators may sleep for about 20 hours, but they are called short sleeps where it is easy to have a sleep break because cats, although asleep, have a great willingness to react faster than you can if you were awake.
How long does the giraffe sleep?
Giraffes have a sleep pattern that is the strangest among other animals. The young giraffe sleeps, bending the legs under her bodies that serve as her pillow! The adult giraffe rarely sleeps in this pattern but sleeps for only a few minutes, and does not exceed five minutes of sleep. Mostly she may sleep fully parked, with half open eyes, and ears continue to move. On average, the giraffe sleeps for 30 minutes during the night and is the shortest sleeping period in the animal kingdom.
Why did the giraffe sleep less?
The interpretation of the Giraffe's short cycle sleep lies in the fact that large animals lying in the forest may be a tempting prey for predators, especially since they do not have thick skin that acts as a shield, nor have sharp teeth to defend themselves. So she remains in a state of readiness for a possible attack; she stands with her eyes open, which may help her escape, as she has the ability to run 56 kilometers / hour.
Sources:
http://www.thomsonsafaris.com/blog/sleeping-habits-of-giraffes/