It was the day before March's Quidditch Match and I decided to practice spells on some pebbles in the Training Grounds as it was still 2 hours before the match. When I got there, I saw Grace Kennedy, a sixth-year and the Ravenclaw Keeper, picking some three-leafed clovers.   
"Hey, Grace."  
"Hey."  
She sounded really serious.   
"What's wrong?"   
"There's an illness going around. Even Madam Pomfrey has no idea what is it. These clovers should cure it. Luckily, it's not that bad right now."   
"That's good. I'm going to go to the Common Room to practice spells. See you at the match!"   
"See you at the match!"    
When I got into the Common Room, there was a small notice which read:    
Quidditch Players and Spectators    
Today's match against Slytherin will be cancelled due to serious cases of an unknown illness. The match will be moved to the 20th of the nearest possible month.  
Sorry and thank you,    
Madam Hooch and Madam Pomfrey    
Some people groaned, most people looked concerned at the illness.    
"What will I do!" Sebastian moaned. "I had practised my commentary for weeks!"   
"One." Melody shouted. "How can you practise commentary? Two. If Madam Pomfrey can't identify the illness, it's serious."   
"Y-yeah." Stuttered Sebastian. "That's e-ex-exactly what I meant to say."  
Melody opened her mouth but Grace then came in the room with a pot the size of a butterbeer glass which was filled to the brim with clovers.  
"Woah." I stared at the clovers. "It took you about five minutes to get all that?"   
"Well, I used the Severing charm to cut about ten clovers at a time." She admitted.   
"Why are you here?" Asked Dylan. "You should give them to Madam Pomfrey right now. Quidditch has been cancelled by the way."  
"That's a shame. And I am going to give give this to Madam Pomfrey, I just wanted to check none of you have Kennedy's Brew."  
"Kennedy's Brew?" Asked Leona.  
"Y-yes. It's what I called my healing potion." 
"Nah, nobody has it." Dylan said.    
"Oh, I left it in the dormitory." She gasped suddenly.