Out of the 4 stages of sleep, NREM-1, NREM-2, NREM-3, and REM, the third stage is where the brain will emit delta waves. These waves are large and slow, as such, this stage of sleep is also known as slow-wave sleep. It is during this stage where it may be difficult to wake someone up.

Dreaming has been observed during REM sleep. Brain waves at this stage resemble the brain waves of an individual who is awake. The person's heart rate will increase as well as his or her breathing. Every few seconds, the individual's eyes may be observed darting from side to side. This movement signifies the beginning of a dream.

While the recuperation explanation may seem like a good answer, it cannot be considered a theory on its own.

"Sleep protects" is a theory that a species will adjust its sleep pattern in a manner where it is optimal given that species niche, or environmental context. For instance, if an animal has a limited ability to hide from its predators, it may sleep less.

Sigmund Freud is well-known for his ideas of psychoanalysis—where an individual's personality is based on childhood memories. He is particularly famous for his concept of childhood progression through psychosexual stages. During the id phase, a child is consumed by his desires and need of instant gratification. Freud theorized that once a child graduated from the id stage, then he will achieve the ego stage and ultimately superego. At this time, the adult will have buried and overcome his desires in his unconscious and be able to pay attention to the conscious thoughts associated with morally and socially acceptable behaviors. Given this information, Freud would most likely be in support of dreams serving the purpose to satisfy one's wishes. He believed that dreams provided a platform to act out an individual's latent content—buried unconscious wishes and desires—in a censored symbolic version by way of manifest content. Manifest content is what the individual will remember as the dream's content and main storyline (i.e. what the dream was at "face value").

Dreaming has been observed to predominantly occur during rapid eye movement (REM) sleep. A dream may be noted at the beginning of REM sleep. If dreaming is to serve one function of reorganizing information into memory, then as some studies have indicated, uninterrupted REM sleep is most beneficial for integrating new information. Given that no stage 5 sleep has yet been identified, this would be an incorrect answer. Although some studies may counter-argue that interruptions in non-REM stages will yield poor memory integration, it is important to remember that a majority of dreaming does not occur in these stages.

Theta waves are usually connected to emotions, memories, and other activities in the limbic system. These cognitive processes calm when a person is transition from awake to stage 2 of sleep; therefore, the waves will be less frequent and higher in amplitude.

REM sleep is characterized by all of the listed answer choices except slower brain activity. REM sleep helps us remember more and is the stage of sleep where dreams occur. Our brain activity is actually intensified during this stage.

The activation-synthesis model of dreaming suggests that during REM sleep, different neurons in different brain areas randomly fire (possibly to keep the brain active and “working”). The brain interprets these random neural signals, which largely come from areas associated with emotion and memories like the limbic system and hippocampus, and attempts to shape them into coherent perceptions of the information being passed by these sensory neurons. We experience this shaping as dreams. 

Hypnosis, meditation, and recreational drugs are all methods to induce an altered state of consiousness. These do not occur naturally, and require proactive involvement by the subject. There are, however, altered states of conciousness that occur completely naturally, such as sleep, daydreaming, or even altered states that can be caused by sleep deprivation. 

The effects of hypnosis have the potential to last long after the session is over. 

All individuals react differently to hypnosis and the effects are difficult to predict. Though it can reduce inhibitions, hypnosis cannot force a subject to do something they normally would not. Also, hypnosis is not a reliable method of extracting repressed memories, and there is no evidence to suggest it will allow one to remember past lives.