Is the ringing/tinnitus a new symptom? Seemingly innocuous viral infections and other problems can cause sudden and/or permanent sensorineural hearing loss. Oftentimes people don't realise this and don't get treated promptly because they assume the poor hearing is due to congestion from a routine illness (and the treatment window can be quite short for SSNHL). It's good that you have an appointment tomorrow, but err on the side of caution and don't delay further. I don't know where you live but depending on what country, ideally you go into the ENT's office with an audiogram in hand from an audiologist, since they will absolutely need or request one for a diagosis and many cannot/do not do basic audiometric tests and will just refer you to an audiologist in the first place, and then schedule you for another appointment which may take end up taking many more days or even weeks- where the effectiveness of most treatments for SSNHL begin to plummet.
Stay hydrated, avoid strenuous physical activity, discontinue caffeine, any stimulant nasal decongestants, or antibiotics you might have been taking for your illness. Still follow up with treatment even if your hearing suddenly seems like it gets better, because that is also a common sensation in sensorineural hearing loss.