Each person has an innate blockage against external influences on the mind, but it is easily removed, there are several methods. I doubt that someone from the practitioners will tell you about them.
During hypnosis, a person receives a suggestion from the hypnotist, through which the hypnotist has an associative series of sensations associated with the natural state of trance for each. Trance is a state, and hypnosis is the process of going into a trance state. The hypnotic's acceptance of the operator's suggestions inhibits his cerebral cortex (excitation processes attenuate with the exception of the "rapport zone"), which gradually deepens the trance state and at the same time enhances the acceptance of suggestions.
Firstly, the very statement of the question is not entirely correct, because trance and hypnosis (and, for example, meditation) are literally the same thing.
This is a separate physiological state, different from sleep and from wakefulness, contrary to the popular outdated opinion that it is "half-asleep", etc.
The condition for the transition to a trance state is a hypnogenic situation (a special combination of psychological, motor, sensory stimuli). The realization of a hypnogenic situation is perceived by the body as eustress, as a result of adaptation to which specific physiological changes occur, which in a very simplified way can be called a state of relaxation.
This specific state has many interesting consequences - for example, increased blood pressure, as a rule, decreases (and even vice versa), chronic pain either passes or decreases, etc., in other words, we can say that in a state of hypnosis, the body strives for some self-regulation, as much as possible. Accordingly, you can find a bunch of specific and not very correlates - from the side of the electrical activity of the brain (using an electroencephalogram), from the side of the activity of the autonomic nervous system (for example, heart rate variability). One of the properties of a hypnotic state is an increase in suggestibility and learning, which is what insidious psychotherapists use).
One-piece wagon explanations. Here's another one for you. Your perception (hearing, sight, touch, etc.) is your usual signal source. But. During sleep, you can "turn away" from this signal and perceive another source, that is, sleep. So, exactly the same thing happens when you enter a trance. Reconstruction of perception to other sources. Your nervous system is full of these sources, both for generating dreams and for trances. Call it whatever you want, but the mechanism is one. Now in this direction, slowly and reluctantly, like all scientists carefully, they are digging into the Visceral theory of sleep. No loud statements. Feel free to explore at your leisure, curious.
When I enter Bitrix 24, a list of companies is displayed under the name (where there are now stripes), the next time I enter the companies, what is the reason?