Such a basic logical fallacy, I'm surprised you would make such a mistake.
It's not a logical fallacy at all.
Like many other quasi-scientific fields of "study", hypnotism makes a specialized language out of ordinary, established terms, giving them new and different meanings. The ubiquitous "suggestion", in the context of hypnosis, is one of the most common such examples that can be found to illustrate this.
To be sure, "suggestion" is a real thing. Asking a (conscious, alert) person at a party if they remembered to lock up before they left the house for instance, has a chance of planting a suggestion in a person's (not just the asked person, but anyone who hears the question - including the person who asked it) mind that they may not have done so - a suggestion that might cause growing concern for as long as a person is unable to verify whether they have. But this isn't the kind of suggestion hypnotists talk about.
Earlier you posted links to a couple of alleged procedures for assessing a person's level of "suggestibility", used by people who happen to be studying hypnosis at Harvard or Stanford or some place. The procedure, which to me seems indistinguishable from just about any other hypnosis session, simply involves "hypnotizing" a person and asking them to do a set of specific things. The documentation calls these things
suggestions, but they very certainly are nothing of the kind. When you tell someone to "raise your hand", that's not a "suggestion", that's an instruction. A person who then raises their hand, is not "responding to a suggestion", they're complying with the instruction.
The list of arbitrary and whimsical instructions goes on; but the test is fatally flawed for one glaring reason, and that is that there's nothing special about these instructions that would allow a therapist carrying out the procedure to distinguish between a so-called "hypnotized" person and a compliant, fully conscious person.
For instance, one of the instructions is to imagine that your arm has through some means been stiffened and immobilized so that you can't bend it at the elbow. You are
instructed to imagine this scenario, and then
instructed to attempt to bend your arm, while imagining it is not possible.
Now,
anybody can consciously do this. I can imagine that there is a great stiffness in my elbow, and that I cannot bend my arm when I try. I can even try extremely hard, to no avail - and I can do this so well that my arm and then shoulder actually tremble with the force of effort. My arm muscles (such as I have...) bulge and strain. My face becomes flushed and red, a sign that my blood pressure is rising. My body can produce these
physiological effects as a result purely of my imposing an imaginary inability to bend my elbow. And then instantly, I can release the imaginary immobility, and bend my arm with no effort at all. I can even do this whilst struggling, so that my arm closes suddenly with great force as the rigidity instantly vanishes. And I can do this completely consciously, without needing an altered mental state.
The same is true for other instructions given, such as one to imagine that you are a young child again sitting in your second-grade classroom, and then answering questions within the context of this scenario - what grade are you in, how old are you, what is your teacher's name, and so forth. Again - not something any conscious person has even the slightest trouble doing.
And we're not even talking about "deception" here, or "pretending to be hypnotized". I can walk into the person's office and sit in his chair, and with no attempt to deceive whatsoever - I can make positive, good-faith attempts to
simply follow all of the instructions as given with no resistance to the process whatsoever: first to feel increasingly relaxed and calm, and to close my eyes as directed; and then to start raising my arm as told, imagining that it is unbendable, pretend I'm a young child again and answer questions within that context until told to stop imagining that scenario, and so on and so on through the long list of instructions...all fully consciously, and willfully, and according to that test's results I am a highly hypnotizable and "suggestible" person. The therapist will conclude that I was "hypnotized" and "responding to suggestions", because there is no way to tell the difference. The test is absolutely useless.