Can be post operative sensitivity. Since the cavity was really deep, more dentinal tubules (small tubular structures in the tooth tissue that contain dentinal liquid and odontoblastic processes (which are connected to the A delta nerve fibers) and their diameter increases. So deep cavities involve large and a lot of these structures. Thus, stimuli can have a bigger impact on the pain development. As soon as a stimuli hits the tooth/open dentin, it causes movement of the dentinal liquid which is transfered to the nerve and then causes pain.

Do you know if your dentist used some kind of pulp protection? In very deep cavities, bonding is not enough to really seal the tubules and protect pulp and an RM/GIC liner should be used.

Anyway, post op sensitivity decreases in dynamics and is usually completely gone after 2-3 weeks.