Sirius would probably be very worried and immediately try to help Harry. He might use some basic healing spells he knows.
Sirius would be in a state of panic at first. But then he would quickly gather his wits. He'd likely try to find out what caused the seizure, whether it was a spell, a potion, or something else entirely. He might also call for Remus or other trusted friends for assistance, as he wouldn't want to leave Harry alone in such a vulnerable state.
Chapter 814, "Under the Eaves, One Must Bow", is the clearest early answer because it turns Lin Manru's situation into a concrete plot event.
Chapter 521, "Stick to One Line of Work", is the clearest early answer because it turns Younger President Jin's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jin Siyue had exhausted a great deal of effort to finally get through...
Chapter 457, ""Back Against the Wall", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Five minutes later, he stared at Yu Li with his twitching mouth...
Chapter 725, "Still Want to be the Second Young Master of the Jiang Family!", is the clearest early answer because it turns Xu Ning's situation into a concrete plot event.
Chapter 360, "There's No Shame in Wearing a Dress Designed by Your Mother", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, Jiang Li showed no fluctuations in emotion and remained unperturbed....
Chapter 531, "She Really is a Remarkable Person", is the clearest early answer because it turns Crown Prince's situation into a concrete plot event.
Chapter 690, "Miss Jiang, Marry Me!", is the clearest early answer because it turns Miss Jiang's situation into a concrete plot event. A useful checkpoint is the way the scene starts with No wonder she had predicted she would come into some unexpected...
Chapter 744, "Dig Three Feet into the Ground to Find Her!", is the clearest early answer because it turns Mrs's situation into a concrete plot event. Early on, What?!" Wen Jiaojiao directly questioned out loud, "On what basis are.... By the end, Where have you taken my wife?.
Chapter 394, "I'll Invest One Billion in Your Movie", is the clearest early answer because it turns Shang Shaobai's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Li said, "You don't need to question it, just do as I say, and...
Chapter 586, "She Just Likes Men Who Show Weakness Initiative", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Jiang Yan quickly swam over to the person.