You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of Danny Phantom fanfictions, and you can use the search function to specifically look for ones related to Danny being sick. Another option is FanFiction.net, which also has a decent number of Danny Phantom stories, though the search might require a bit more effort to narrow down to the sick - themed ones.
Some Danny Phantom fan communities on social media platforms like Tumblr or Reddit can be a good source. Fans often share links to their favorite fanfictions, including those with a sick Danny Phantom theme. You can also join Danny Phantom - specific forums where fans discuss and recommend different fanfictions. Just make sure to follow the community rules when asking for or sharing links.
Chapter 346, "Elite Warriors, One Against Three, The Cause of the Beast Tide [10,000-Word Chapter, Continued Tomorrow]", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter turns that into something concrete by moving from Nowadays, any of these six armies alone, placed five years ago, would... to Thus, in Great Xia, it's a comparison of who breaks through more....
Chapter 97, "Can This Really Be Broadcast?", is the clearest early answer because it turns Be Broadcast's situation into a concrete plot event. It opens with Suddenly, Jiang Li's livestream room was packed with people, and the... and closes on And you believe what she says?.
Chapter 317, "Wrapping Up the Migration, Great Xia's Flourishing Scene, Star-picking Hall", is the clearest early answer because it turns Li Xuanling's situation into a concrete plot event. The setup is Second Year of Great Xia, September 30, First Half of the Night..., but the pressure keeps building through From the northern city wall of Xia City, a slight rumble suddenly....
Chapter 341, "Moao's Nine Towns, the Inspection System and Zhenyu, Li Hu and Hong Yuru", is the clearest early answer because it turns Moao Mountain Range's situation into a concrete plot event. The chapter gives readers a real answer by opening on The entire Moao Mountain Range stretches from northwest to southeast. and ending on The powerful northern Three Towns block the north..
Chapter 308, "Shocking Turn, Grave Injuries, and Restless Hearts", is the clearest early answer because it turns Long Fist Form's situation into a concrete plot event. The setup is But the Li Xuantiang in front of him was different., but the pressure keeps building through This strike could truly make him sense danger!.
Chapter 306, "Rebel Collaborators, Chaos and Opportunism, Long Mountain Changes Hands", is the clearest early answer because it turns Li Xuanling's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Xia Hong's expedition to the north never intended to capture Long... and follows through with That Golden Armor Army from Great Xia hasn't moved yet; they've been....
Chapter 84, "Is it Just About Having Hands?", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter gives readers a real answer by opening on When the villagers tasted his curry beef one by one, their faces...
Chapter 293, "The Lion Hunts the Rabbit – Luring the Enemy and Falling Into a Trap (Part 3)", is the clearest early answer because it turns Li Xuanling's situation into a concrete plot event. The chapter gives readers a real answer by opening on Li Xuanling remembered very clearly, at that time the scout reported... and ending on Li Xuanling perked up, watching her cousin Li Xuanqiu hastily....
Chapter 40, "The National Museum Speaks!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with [Jiang Li claims she copied this herself?
Chapter 63, "Far Exceeded Expectations!", is the clearest early answer because it turns Jiang Shixu's situation into a concrete plot event. Early on, During those seven days, he thought he had completely escaped from....