While we need to sleep 7-9 hours per day, almost 40% of us sleep less than the minimum amount. As an example parents of a newborn child sleep 450-700 hours in their first year of parenting. Watch this amazing video to learn more about sleep:

REM sleep occurs in bursts totalling about 2 hours a night, usually beginning about 90 minutes after falling asleep.
Dreams, once thought to occur only during REM sleep, also occur (but to a lesser extent) in non-REM sleep phases. It’s possible there may not be a single moment of our sleep when we are actually dreamless.
REM dreams are characterised by bizarre plots, but non-REM dreams are repetitive and thought-like, with little imagery – obsessively returning to a suspicion you left your mobile phone somewhere, for example.