Final answer:
The described symptoms of overwhelming and irresistible attacks of sleep indicate the sleep disorder known as narcolepsy (option b).
Step-by-step explanation:
A client who experiences overwhelming and irresistible attacks of sleep is most likely suffering from narcolepsy. Narcolepsy is a sleep disorder characterized by a person's inability to resist falling asleep at inopportune times. These episodes can occur with other symptoms such as cataplexy, which is muscle weakness, and hallucinations similar to those during REM sleep. It is important to recognize and treat this condition as it can affect everyday activities and the overall quality of life. To answer the question, b) Narcolepsy best describes the sleep disorder with the symptoms provided.