Your relationship to the person on whom you are spying matters. If that person is your child or your employee, you have a lot more leeway when it comes to monitoring their activities. If you think someone is spying on you illegally, file a report with local law enforcement so they can investigate your case.
Most cats snooze around 16 hours per day. The majority of their sleep time, however, is much shorter than the typical seven hours or so that humans average at. night. Cats tend to sleep lightly, without going into a deep sleep.
In sleep, as in all things, cats are highly individual. Some cats sleep less than 16 hours a day and some sleep more; some spend as much as thirty or forty percent of their sleep time in a deep sleep cycle (this is particularly true of older cats).