Is weakness from antipsychotics even after discontinuing due to a movement disorder or is it just because so many things in brain have changed. ?

Not necessarily.: Antipsychotics have side-effects that include tiredness, sleepiness, and even depression which could be mistaken for weakness. The movement disorders like pacing, tremors or lack of movement are side-effects also which will disappear over a period of time after you discontinue them, depending on the half-life of the medication.