There seems to be a lot of assumptions about adult-onset deafness. The first assumption is that adults become hard of hearing due to age, therefore anyone who loses their hearing as an adult becomes hard of hearing. In addition to hearing loss associated with aging, known as presbycusis, there are many other ways adults become deaf. For my convenience, I made up four groups.
Some medical losses can be equally sudden.
These are not mild and moderate losses. With surgery and some injuries, damage to the nerves leaves no sound perception at all. With surgery, there may the advantage of some advance warning, but with sudden loss you go from hearing one day to deaf the next. Progressive losses may be detected at the hard of hearing stage, but either slowly or suddenly cross over the line to become deaf. But there is also more chance to deny the existence of the hearing loss or the degree of the hearing loss, since the change is so gradual it goes unnoticed.