Do not worry because most cats sleep about 16 hours a day. This is normal because the cats are natural predators and hunt mainly at night. The cats are most active before the release and before sunset.
Cats frequently change activity during the day. Instead, most of the day to spend sleeping, they replaced it with naps.
Cats have two stages of sleep. While under easier cats can awaken the slightest sound, and they at this stage of sleep spend almost 12 hours.
While the cat is in a phase of deep sleep, she sleeps deeply and this phase is very dangerous for their growth on the body and its recovery.