An interesting question!
How we experience the hypnotic trance is state-dependent, meaning whatever state of mind you're in, can influence the depth, intensity, and duration of any trance experience. Essentially, it is reaching that nebulous state that exists in sleep-states and consequently creates a bridge between the world of emotion and cognition!
Primarily we are emotional beings and secondly cognitive ones. However, we have a compulsion, if not a need, to make conscious sense of our subconscious processes, even though we have no idea what they actually are! So much of life's difficulty arises out of our conscious and non-conscious subjective interpretations of life's feelings. One may say "I feel a little apprehensive," another, "I feel terrified." Our linguistic ability to describe feelings accentuates a direct communication (external and internal) between our understanding of words and the inherent implication at the level of emotion. Simplistically meaning there's a link between the words we use and our emotional understanding of them. This also applies to body language and facial expression. Since emotion elicits cognition and cognition elicits emotion, there must be an interface between the two. Scientists believe this to involve many brain regions. For example amygdala, hippocampus, hypothalamus, thalamus and the extended amygdala (including the central medial amygdala, sublenticular substantia innominata, nucleus accumbens shell, bed nucleus of the stria terminalis. Quite a collection!
Hypnosis works by stimulating the sensory cortices that are involved in both cognitive and emotional processing. Essentially communicating with the brain, via the auditory cortex and stimulating our other sensory regions both directly and remotely. Hypnosis occurs when the brain is in specific phases of brainwave activity i.e. theta/REM/NonREM2, 3. These neural oscillations are further modulated by PGO waves and a reduction of norepinephrine from the locus coeruleus (the precursor to the stress response). Hypnosis creates an almost identical state to that of nighttime sleep. Nighttime sleep facilitates the necessary changes in gene expression, which create an alteration in the way memories are both restored and activated (consolidation and reconsolidation). It is this top-down, bottom-up process which eventually adapts the responses at deep brain levels to meet the clients' desired outcomes. Hypnosis is an integral part of a very complex biological process and that just demonstrates how amazing the brain actually is! It is primarily a part of how and why language allows us to reprogramme the way our brain functions. Evidence to support that can be felt when someone says something very pleasant or very unpleasant to you, either can elicit great changes in the way we feel! To find out more about how hypnosis works, please go here.
Lastly, I often hear other hypnotherapist say, that you have to get to the source of the issue, aka the initial sensitising event. I disagree with this because some of the issues we face are consequential of events that occurred when we were very young. Maybe before we could even speak or while we were still in the womb! How could this be? Well, take someone with a spider phobia. The unborn child experiences the mother emotions, it hears the world outside nut has no context. During gestation, it's likely the mother will have a phobic response to a spider, the baby experiences fight or flight, it feels the gyrations, hears the noises. But obviously, it but has no idea what's going on. After birth, baby observes its mother have the phobic response, sees the gyrations, hears the screams of terror and will likely go into fight or flight itself. However, it still has no idea what is going on. Then some years later, it discovers, observationally, that the object of this abject terror, is this tiny little 8 legged thing called a spider . . . and a phobia is born! Well if I don't know what caused it, how can I ever fix it, you say? I will happily explain all that during the Free Consultation!