Final answer:
Akathisia is the term for the inability to stay still and be free from anxiety, often associated with neurodegenerative diseases and certain medications.
Step-by-step explanation:
The inability to rest, remain still, to remain calm, or to be free from anxiety is known as akathisia. Akathisia is a condition characterized by a feeling of inner restlessness and a compelling need to be in constant motion. This disorder is often associated with a variety of neurodegenerative diseases such as Parkinson's disease and can substantially impact one's quality of life. It is sometimes observed as a side effect of certain medications, especially antipsychotics. Treatment typically involves adjusting medication or prescribing specific treatments aimed at alleviating the symptoms.