Welcome to health care magic forum,
With the details you have given, I can tell you that you probably had a periapical granuloma
or a periapical cyst
. Periapical granuloma or cyst occurs when there is long standing periapical infection. (Periapical infection is the term used to explain infection which involves roots of teeth due to decay or any other reasons). In your case probably it was very large cyst/granuloma and was probably compressing the nerve
beneath it. Now since the tooth has been extracted and the granuloma/cyst has been removed, you've felt instant relief of pressure. But since the extraction wound is still fresh, it is normal for you to feel the extraction site sensitive. Also when a tooth is extracted, the roots of adjacent teeth would be exposed till the wound heals, exposed roots could also be cause for sensitivity. One more reason for sensitivity could be the adjacent teeth might have a decay.
I advice you to wait for few days for initial healing to take place, the symptoms may reduce. If symptoms doesn't reduce even after 2 weeks you need to go back to your dentist
and get examined thoroughly, if necessary you may have to consult oral and maxillo facial surgeon.
Wishing you speedy recovery