have you been to a dr? sometimes if you have a bunch of wax, water can get trapped behind it. if that is the case, the drop in hearing happens suddenly after pool/shower. if you have been sick, it is more likely you have fluid behind the eardrum (which some primary docs claim to "see" but often times they don't see anything and just put you on meds). if you go to an ENT with an audiologist, they can actually run a test that checks that movement of the eardrum, which will change if there is fluid behind it.
how long have you felt like this? the ENT should be able to tell whether the fluid is infectious or not. if it is, you need meds. if it isn't, it can take up to 3 months for it to drain naturally, though a decongestant/anti-inflammatory meds can help to reduce swelling and encourage it to drain.
i would keep up the decongestants - when you tip your head, you are either moving the fluid or allowing some of it to drain down the eustachian tubes. it will take a little time, but it will happen.
but it is possible you are full of fluid. i swear, i've seen primary docs/nurses who "look in my ears" and i would bet a billion dollars that they didn't see my eardrum, bc i know what it feels like. so who knows what she saw.
if it is still like this a month in, i'd see an ENT. but give it a few weeks.