It's not possible to experience more than one level of sleep at the same time. Each stage of sleep has distinct characteristics, such as brain wave patterns and muscle tone, which cannot be present simultaneously. However, some phenomena can occur during certain stages of sleep that may blur the line between them. For example, lucid dreaming can occur during REM sleep when individuals become aware they're dreaming and can control their dreams. Sleepwalking occurs during deep NREM sleep, while sleep paralysis and hypnagogic state occur during the transition between wakefulness and REM sleep. Additionally, if an individual experiences a period of insufficient REM sleep, they may experience REM rebound in subsequent nights where they spend more time in this stage to make up for lost REM from previous nights. Overall, while it's not possible to experience multiple levels of sleep at once, there are various phenomena that can occur within each stage that may be worth exploring further for those looking to understand their own sleeping patterns better.