Normal sleep is very important and largely misunderstood. Sleep is a natural yet complex process that we need in both the right quality and quantity to optimize our health, body and brain performance. To understand sleep disorders, we first need to understand normal sleep.
“Normal Sleep” is composed of a transition period into sleep and then a series of “deeper” stages of sleep. The stages of sleep are Stage 1, Stage 2, Stage 3 and REM sleep:
Stage 1 Sleep
When we first lay down at night and turn the lights off, the period of drowsiness with closed eyes is characterized by “alpha” brain waves and slow rolling eye movements. If someone speaks to you or enters the room during this period of sleep, typically we wake up. We slowly become less aware of our surrounding environment as we transition out of this Stage 1 sleep. As such, Stage 1 sleep is only a small fraction of the total sleep (<5%). This is not a restful sleep period. With large amounts of Stage 1 sleep, a person will not have the feeling of a good night’s rest.
Stage 2 Sleep
Eventually, alpha waves mostly disappear, and progressively slower brain waves begin to occur (Stage 2). Stage 2 sleep is characterized by some unusual brain wave activity – K complexes and sleep spindles. Sleep spindles are interesting to see in the sleep study tracing. Most of adult sleep is this Stage 2.
Stage 3 Sleep
The slowest brain waves and typically the most restful sleep occurs in Delta sleep (Stage 3). Unfortunately, as we age our amount of Delta sleep diminishes. There is a correlation with the thickness of brain cortex and delta sleep. As part of the aging process, it is normal for us to lose brain cells, and lose some of our delta sleep.
Dream sleep (Rapid Eye Movement Sleep – aka REM sleep) normally comprises 20% of our sleep time. We tend to have a new block of dream sleep every 90 minutes - and these dream blocks tend to get longer and more complex as the night goes forward. Most people will wake up in the morning out of their longest and final block of REM sleep. This is why many people might recall their early morning dreams but have no recall of dreams earlier in the night.
There are different expectations for sleep as we age. Primarily, children have a lot of Stage 3 sleep and require significantly longer periods of sleep than normal adults. Some very light snoring can be considered normal, as more than 50% of adults snore. If the snoring is very loud or associated with irregular breathing patterns and pauses (apnea), this is obviously abnormal.