A.T. Robertson Commentary Matthew 25:5

"Now while the bridegroom tarried, they all slumbered and slept." — Matthew 25:5 (ASV)

They all slumbered and slept (ενυσταξαν πασα κα εκαθευδον). They dropped off to sleep, nodded (ingressive aorist) and then went on sleeping (imperfect, linear action), a vivid picture drawn by the difference in the two tenses. Many a preacher has seen this happen while he is preaching.