This is the hardest but shortest phase of labor, typically lasting from 30 - 90 minutes. (verywellfamily.com)
Other than short interval distances, this other short phase too often turns to «long» periods of weeks that often turn to months. (philmaffetone.com)
In humans, sleep is also characterized by brain activity: periods of slow - wave activity are each followed by short phases of Rapid - Eye - Movement sleep (REM sleep). (sciencedaily.com)