Which condition is characterized by restlessness and an inability to remain still?

The condition characterized by restlessness and an inability to remain still is indeed akathisia. Akathisia is often described as a state of inner agitation or restlessness, leading individuals to feel an overwhelming need to move. This condition frequently manifests as an inability to sit still, fidgeting, or pacing, which significantly impacts daily functioning and quality of life.

Akathisia can arise as a side effect of certain medications, particularly antipsychotics, and it is distinct from other movement disorders due to its unique presentation of restlessness rather than involuntary or repetitive movements associated with conditions such as dystonia or tardive dyskinesia. Dystonia is characterized by sustained muscle contractions and abnormal postures, and tardive dyskinesia involves involuntary movements typically affecting the face and limbs but lacks the restlessness seen in akathisia. Pseudoparkinsonism mimics Parkinson's disease symptoms such as tremor and rigidity, which do not include the driving need to stay in constant motion. Hence, the features of akathisia clearly align with the symptoms described in the question.