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.

There are three primary theories of hypnosis.

Non-state, also known as "role theory," claims that hypnosis does not alter one's state of mind. Instead, the person undergoing hypnosis is acting out a particular role for a therapeutic benefit.

State theory asserts that a person does not have any agency in the matter of hypnosis. Rather, they are completely submerged in a different state of mind.

The third theory is dissocation, in which a person involuntarily decides to split their own consciousness.

There is no definitive proof to back up any of these claims, though hypnosis remains a popular way to treat a variety of disorders.

"Highly-suggestible" is the term for people who are more easily hypnotized.

There are many purposeful ways to induce an altered state of consciousness, but some accidental or pathological ones include infections, sleep deprivation, or psychosis. Some others are fasting, epilepsy, or traumatic experiences. An altered state of consciousness due to any of these is often an indicator of either a mental or physical health issue and should be addressed right away. 

Psychoactive drugs are any substances that alter behavior, mood, memory, or perception. Some are stimulants, such as the caffeine found in coffee. Others are depressants, such as alcohol.

Priming refers to a person's ability to more quickly/accurately respond to previously asked questions, whether they remember them or not. This is closely related to the mere-exposure effect, which states that we are more likely to prefer familiar things than unfamiliar things.

Opiates, such as heroin, are drugs derived from the opium poppy. These highly addictive substances are used as mood elevators and painkillers.

Antagonists are a type of psychoactive drug. Psychoactive drugs are drugs that change the chemistry of the brain. There are two types that do this: antagonists and agonists. Agonists change the chemistry of the brain by mimicking neurotransmitters. Antagonists also change the chemistry of the brain, but they do not mimic neurotransmitters. Instead, they simply prevent neurotransmitters from entering receptor sites.

The three categories of drugs that have been established are depressants, stimulants, and hallucinogens. Although an individual may seem lively with a small amount of alcohol, alcohol is actually a depressant. The liveliness comes from the fact that alcohol acts as a disinhibitor. This means it will act to slow down neural processing and brain activity responsible for judgment and inhibitions. As a result, people are more likely to act out in ways that they would not under unaffected judgment and conditions. Barbiturates are tranquilizers. These also fall under the category depressants; therefore, this would also be incorrect.