One common theme is vulnerability. When Snape is sick, his usual tough exterior cracks, and we see a more human side of him. Another theme is the exploration of his past. Illness might be related to something from his past, like an old potion experiment gone wrong. Also, the theme of redemption can be present. As he's sick, others might show him kindness, and he may start to change his ways or be more open to others.
One common theme is vulnerability. When Snape is sick, he's not his usual intimidating self, and this shows a side of him that is often hidden. Another theme is the discovery of hidden kindness. Some characters who might not seem sympathetic towards Snape in the original stories, might show concern when he's ill. For example, students who were always a bit afraid of him could end up being very caring.
In a fanfiction, the sick Slytherin student could be a key player in Slytherin's house politics. Snape has to balance the student's health with the power dynamics within the house. He might use the situation to teach the other Slytherin students about loyalty and taking care of their own.
Perhaps a sick Slytherin student is suspected of having a contagious magical illness. Snape would then have to take precautions to prevent the spread within the Slytherin common room and the whole school. He could be shown as using his potions knowledge to try and find a cure or at least diagnose the problem quickly.
Some 'sick snape fanfiction' stories are really engaging. For example, there are those that show how the Hogwarts faculty tries to heal him when he's fallen ill due to a cursed object. The way the different characters interact with a sick Snape can be really fascinating. It can range from Hermione's attempts to find a cure using her vast knowledge to Dumbledore's calm and collected approach in handling the situation. These fanfictions give a new perspective on Snape's relationships within the Hogwarts community.
One good Severus Snape sick fanfiction is 'The Illness of Severus Snape'. It delves into his inner turmoil as he battles an unknown sickness while still trying to maintain his duties at Hogwarts. The author does a great job of showing his vulnerability, which is a side we don't often see in the original books. It also has some heart - warming interactions with his students who start to see him in a different light.
One great Snape sick fanfiction is 'Snape's Struggle'. It delves deep into Snape's inner turmoil when he falls ill. The story shows how his students react to his weakened state, with some showing unexpected kindness. Another is 'Ailing Snape', which focuses on his attempts to hide his sickness while still fulfilling his duties at Hogwarts. It's a really interesting take on his character.
Snape might use his potions knowledge to brew a remedy for Harry's illness. Maybe he gives Harry a special potion that eases his symptoms and helps him recover faster.
In some fanfictions, Snape might be trying to gain something from taking care of Draco. For example, he could be using it as a way to get in good with the Malfoy family or to gain some sort of advantage within the Slytherin house politics. However, as the story progresses, his feelings might change from self - serving to genuine care.