Read again and mark the sentences as T (true) or F (false). 1 We might feel colder when we're sleeping. 2 It isn't easy to wake someone during stage N3. 3 Our brain is less active during REM sleep. 4 Not getting enough sleep causes problems in the long run. 5 People who get enough sleep may live longer than those who don't. 6 Exercising before bedtime helps you sleep.