hello and welcome to health care magic,
I am Dr Sriram nathan and i Shall try to help you out with your problem.
You seem to have injured your drum when you got slapped. Many people do not realize the danger of a simple slap. In a closed environment of the ear canal
and drum a slap causes such intense pressure that the drum ruptures and causes pain and hearing loss
which you are feeling right now.
Now do not worry and most of the time it gets cured:
1. get an audiometric analysis and examination by an ENT to confirm the finding
2. take a course of antibiotic like amox-clav and anti histamine
like levocetrizine in consulatation with your doctor
3. Do not take head bath for two weeks and after that do not allow any water to enter the ear
4. Do not put any ear drops
Remember that if you keep your ears clean and dry the hole and canal will recover
If any other doubts get back to me
Dr Sriram Nathan