Akinesia is slowness or loss of normal motor function, resulting in impaired muscle movement; literally "without movement" or without much movement. It may result from paralysis or temporary paralysis, also from coma. Akinesia may affect all or part of the body.
Akinesia may be a side effect of most antipsychotic medications. According to the National Electronic Library for Health, "This side effect (which is part of Parkinsonism) usually occurs many weeks after starting antipsychotic medication. Akinesia is characterised by apathy and a decrease in spontaneous movement. This side effect resembles the apathy and slowness associated with depression or the 'negative symptoms' of schizophrenia and hence is sometimes misdiagnosed and left untreated. The drugs that are used for treating acute dystonia are also helpful for treating akinesia."
Reference: National Electronic Library for Health (1999). Extrapyramidal Side Effects.