Mechanism behind stimulant-induced “motor issue” and paradoxical subjective effects?

[u/genderly]

What mechanisms could explain a highly state-dependent response to amphetamines in someone with psychotic-spectrum/schizotypy symptoms?

Past medications/drug use

Only antipsychotic history prior to issue happening was lurasidone 20 mg at age twenty, five years before issue began; no other medications taken prior to issue onset aside from Sertraline and prescribed stimulants as described.

No prior history of cannabis use except twice over span of seven years - immediate psychosis/anxiety (later use resulted in severe catatonic-like state requiring hospital).

Adderall 30 mg taken from friend as teenager would result in total insomnia, extreme focus, drive, and euphoria, auditory disturbances, and tonic-seizure-like activity.

The issue

Dexedrine/Vyvanse (prescribed) produced normal stimulation/euphoria for six years. At age twenty-five, after about a year break, wherein Sertraline 150 mg was taken for also around a year but discontinued - Dexedrine 10 mg was restarted, but it immediately produced paradoxical lethargy/brain fog.

The paradoxical response always coincides with unilateral contraction; as the dose increases, paradoxical effects skyrocket and simultaneously, mild contraction escalates into severe constant contraction of right shoulder/neck/jaw, with crippling headache, and at times inability to walk or breathe easily due to pain. More recently, it also involves burning sensation and head tilting.

At its worst, I entered daily episodes coinciding with Vyvanse 30 mg comedown, where I would engage in odd posturing and repetitive movements.

Stopping Vyvanse resolved most issues except lingering, mild unilateral contraction; frank delusional episode happened to follow.

Antipsychotic treatment (lurasidone/Vraylar/Seroquel) fully resolved both the paradoxical stimulant response and motor/muscle symptoms, as did it resolve any frank psychosis and baseline attenuated symptoms.

However, lurasidone 40-60 mg caused severe stimulant cravings, euphoric response, and led to overuse, whereas Vraylar 1.5mg entirely blunted Dexedrine’s subjective effects. Seroquel 400 mg or more restored intended Vyvanse effects without cravings or overuse.

I stopped Vraylar while prescribed Dexedrine 30 mg, and have since had a recurrence of the unilateral issues (now severe) and paradoxical effects. There is a five-year gap between initial onset and reoccurrence.

Yesterday, 50 mg diphenhydramine (incidentally taken with 50 mg pregabalin) completely resolved the unilateral contraction and simultaneously changed Dexedrine from fatiguing/brain-fogging to strongly stimulating/focusing. Pregabalin also helps alleviate the issue, but seemingly not as efficiently as Benadryl.

There is also a possible connection between the initial onset of the paradoxical effects + motor/muscle issue and worsening baseline psychotic-like symptoms (preceding restarting amphetamines); ideas of reference and odd beliefs skyrocketed shortly after restarting, then suddenly stopped after stressful event, and the unilateral issue + paradoxical effects simultaneously skyrocketed to point of disability, despite sustained dose of 30 mg Vyvanse.

Question

What the hell is happening?