I suffer from Ménière’s disease, so I often get dizzy.
The reason I haven't been able to get further than Level 1 on WaniKani must be because I have "can't-learn-foreign-language" syndrome.
Don’t make a big deal out of what he said. It’s definitely a lie that he’s suffering from an incurable disease.
As you can probably imagine, when you add the kanji sick to another word, you're saying what kind of sickness it is; you are mentioning what disease it is.
Since this is attached to other words, it's treated like jukugo and gets on'yomi treatment. This is the reading you learned with the kanji.