‘Then I came to those of the captivity at Tel-Abib, who dwelt by the River Chebar, and to where they dwelt. And I sat there overwhelmed among them seven days.'
At some point the Spirit released him, and he then made his way back to the settlement of his fellow-captives. And for seven days he sat there ‘overwhelmed'. The word means ‘appalled, desolated' and the causative conjugation signifies that it was the effect of what he had experienced. It took him ‘seven days' to recover, longer than just a few days.
(‘Seven days' generally signifies a longer period than the shorter ‘three days', two stereotyped expressions. ‘Three days' would mean anything from one and a half days to six days, ‘seven days' would indicate a little longer period. Compare the use in Genesis for ‘three day' and ‘seven day' journeys).
It is perhaps significant that seven days was required for the consecration of a priest (Leviticus 8:33). It could be that he saw this as his period of consecration to his mission.