Too much sliding down the Ramparts?

Quote	Source
Standing against the ramparts, very white in the face, Dumbledore still showed no sign of panic or distress. He merely looked across at his disarmer and said, "Good evening, Draco."	Page 584
"Yeah, well, you still didn't realize who was behind that stuff, did you?" sneered Malfory, as Dumbledore slid a little down the ramparts, the strength in his legs apparently fading, and Harry struggled fruitlessly, mutely, against the enchantment binding him.	Page 587
"Isn't that the secret method of communication the group that called themselves Dumbledore's Army used last year?" asked Dumbledore. His voice was light and conversational, but Harry saw him slip an inch lower down the wall as he said it.	Page 589
"Yes, I do," said Dumbledore, and Harry saw his feet slide a little on the floor as he struggled to remain upright.	Page 589
Malfoy was showing less resolution than ever. He looked terrified as he stared into Dumbledore's face, which was even paler, and rather lower than usual, as he had slid so far down the rampart wall.	Page 594
...at that precise moment, the door to the ramparts burst open once more and there stood Snape, his wand clutched in his hand as his black eyes swept the scene, from Dumbledore slumped against the wall, to the four Death Eaters, including the enraged werewolf, and Malfoy.	Page 595

Source: Half-Blood Prince, Chapter 27, The Lightening Struck Tower