Suggestibility is a clinical features of certain mental health issues, such as Histrionic Personality Disorder (HPD), Paranoid Personality Disorder (PPD), Borderline Personality Disorder (BPD), Schizotypal Personality Disorder, Bipolar Disorders, and Psychotic Disorders.
Suggestibility is often comorbid with impaired reality testing and a pronounced fantasy life bordering on a delusional disorder. Patients with this profile are very amenable to a wide spectrum of cues, including subliminal and body language ones.
Some suggestible patients try to please their therapists: they fake expected behaviors and they collude in or originate a shared fantasy with the clinician.
The shared fantasy involves both transference and countertransference. The therapist is coopted into becoming an active participant in the contamination and compromise of the therapeutic process thus undermining the therapeutic alliance.
Boundaried therapists should prevent this from happening. But, regrettably, some of them don’t because it caters to their own psychological emotional needs and to their cognitive distortions (such as grandiosity).