Adam Clarke on Judges 16:19

She began to affect him - She had probably tied his hands slyly, while he was asleep, and after having cut off his hair, she began to insult him before she called the Philistines, to try whether he were really reduced to a state of weakness. Finding he could not disengage himself, she called the Philistines, and he, being alarmed, rose up, thinking he could exert himself as before, and shake himself, i.e., disengage himself from his bonds and his enemies: but he wist not that the Lord was departed from him; for as Delilah had cut off his locks while he was asleep, he had not yet perceived that they were gone.