Perhaps there is some sort of magical artifact or potion that has an unexpected reaction on Harry. In the fanfiction world, there could be a new, untested magical item that Harry comes into contact with, and it has a negative impact on his magical core or nervous system. This could lead to a seizure, and it just so happens to occur in front of Snape, who might then be in a position to either help or suspect Harry of something more sinister.
One reason could be that Harry is under an extreme amount of stress. He has so many burdens on his shoulders in the wizarding world, like fighting Voldemort. This stress could manifest physically as a seizure, especially if he is in a tense situation in front of Snape, who is often a source of anxiety for him. For example, if Snape is about to accuse him of something he didn't do while he is already worried about other threats to the wizarding world.
Chapter 328, "Unexplainable Unease, Jade Dew Stone, Li Xuanling's Panic (Part 2)", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. It opens with Through the harvest after killing Wu Xiong and Li Xuantian, Xia Hong... and closes on Her whole face turned red in an instant, instinctively wanting to....
Chapter 335, "Songyang Ridge, Seven Houses Surrender, First Batch of Silver Arrives", is the clearest early answer because it pushes Songyang Ridge into a new phase or setting. It opens with It seems you all came prepared today. and closes on Lord Xu, our Great Xia's expansion and annexation outward is.... The key payoff is that it turns Songyang Ridge's growth into a concrete upgrade step and sets up the next payoff in the relationship tension storyline linked to Xu Ning.
Chapter 335, "Songyang Ridge, Seven Houses Surrender, First Batch of Silver Arrives", is the clearest early answer because it pushes Songyang Ridge into a new phase or setting. A useful checkpoint is the way the scene starts with It seems you all came prepared today. and follows through with Whether they remain to serve the Lord will entirely depend on Lady's....
Chapter 239, "Shifting Situation, Great Xia Special Envoy (Part 4)", is the clearest early answer because it turns Long Mountain's situation into a concrete plot event. Early on, Is there a young Cold Resistance Level?. By the end, I hope the people of Long Mountain are aware of this!" After these....
Chapter 301, "Long Mountain Enters, Resists the Enemy to the Death", is the clearest early answer because the violence around Hundred Forged Armor becomes final instead of hypothetical. The chapter gives readers a real answer by opening on Entering the construction area, everyone immediately noticed that the... and ending on Great Xia wiped out the two Longyou armies, with 800 new sets..
Chapter 207, "Improving Corvée, Changes in the First Year [Happy New Year!]", is the clearest early answer because it turns Xiang Liang's situation into a concrete plot event. Early on, With the abundant resources of Great Xia, breaking through to the.... By the end, The iron mine in this valley is nearing depletion, and these people....
Chapter 259, "Tasks, Helplessness, Ongoing Screening (Part 2)", is the clearest early answer because it turns Xiang Liang's situation into a concrete plot event. The setup is Like him, there are twenty-eight other people who took on this task., but the pressure keeps building through Above them is a captain who will reward them with varying....
Chapter 336, "Cultivation, Enlightenment Lotus Platform, Major Building Upgrades", is the clearest early answer because Xia Hong finally turns buildup into a real advancement. A useful checkpoint is the way the scene starts with This is not a baseless speculation, the rodents in the Beipo Silver... and follows through with [Currently unlocked buildings 7: Cold Ruins Tripod (Level 4), Martial....
Chapter 226, "Beehive Incident, Lin Ye Is Dead", is the clearest early answer because the violence around Wang Long becomes final instead of hypothetical. The chapter gives readers a real answer by opening on The forty-eighth year of Longyou, April 15th The day of the scheduled... and ending on Hou Ying, stop playing, quickly lead people to the main zone, if we....
Chapter 290, "Bountiful Harvest—Store Land or Store People", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The chapter turns that into something concrete by moving from Entering the Wushuang Realm, realizing that Long Mountain could no... to Even Xia Hong couldn't help but have a momentary daze in his gaze..